1. Definition.
Is a Greek word, which, in strict etymology, signifies that which discourses of nature; but in its common use, it is restricted to that branch of physical science which treats of the different functions and properties of living bodies; while by living bodies are meant those which are by a certain organized structure enabled to grow and propagate their kind.
By this definition, physiology must necessarily have for its object the explanation of that internal organic economy in plants and animals, which nature has devised for the preservation of the individual, and for the continuance and propagation of the species.
It is naturally divided into two kinds, particular and general. The former treats of the properties and functions of the individual or species, as may be seen in the article ANATOMY; the latter is the subject of our present discussion, and treats of those functions and properties which are general or common to all living bodies.
To the genuine naturalist no subject presents such a field of amusement and instruction. When as complete as the state of contemporary science will admit, it will exhibit a general result of all those experiments and observations that have purposely been made or occasionally contributed to illustrate the phenomena of animated matter; and when it shall reach that summit of perfection to which the efforts of genius may carry it, it may be enabled to diffuse a light, of which the naturalist of the present day can have no just or adequate conception: Particularly in phyletic anatomy, botany, and in natural history, its happy effects may be numerous and great. On many occasions it may there introduce order for confusion, certainty for doubt; and may be expected to enthrone science in various places which are now occupied by fancy and conjecture.
Of all the branches of physical science it certainly makes the nearest approach to the region of metaphysics; but yet there is a difference between these, though it may not be very easy to point out the precise line of termination. Physiology, as already defined, being that science which has for its object the organic economy of living bodies, the word organic, we think, here should mark the distinction.
Wherever the economy of living bodies indicates design, and cannot result from any combination or structure of organs, it must be supposed the effect of something different from matter, and whose explanation belongs to that which is called metaphysics, or which we might term the philosophy of mind. By ascribing indeed to the glandular contents within the cranium and to that fiction animal spirits, the motives of action, the preliminary superficial and ill-informed may have been led to an opinion that perception, memory, and imagination, are the functions of the cerebrum; the medulla oblongata, and cerebellum; that the soul is a consequence of organization; and the science which treats of it only a particular branch of physiology. But mind and its faculties are now so well understood and investigated, that this opinion can seldom prevail but where penetration is not remarkable for its acuteness, or where reflection, reading, and research, have long been confined within the limits of a narrow circle.
Instead of mind being the effect of organization, we readily allow that every living system of organs supposes mind, and that in the study of such systems the physiologist must often meet with many phenomena that are less singular than simple perception, and yet for which he cannot account by any knowledge which he possesses of organic powers. This truth we partly acknowledge, when, like ancient Athens erecting her altars to unknown gods, we retreat to those asylums of ignorance, the vis insita, the vis nervosa, the vis vitalis, the vis medicatrix, and a number of others of the same kind.
We choose here to mark precisely the bounds of physiology, because we have always been led to imagine that it would be extremely fortunate for science that all its divisions were accurately defined, that each of them were restricted to its own sphere, where alone it is useful, and were never allowed to make encroachments on the province of another, where its only tendency can be to mislead and subvert all ideas of arrangement.
In its progress of improvement, physiology has been much and often retarded from a want of attention to this circumstance. The time has been when its place was occupied almost entirely by an absurd and ridiculous philosophy, which accounted for everything by an hypothesis, and which pretended to cure wounds a hundred miles distant by a powder of sympathy.
Nay, as if its nature were not yet ascertained, in introductory books whose titles promise much information on the functions of organs, we meet with only a pleasing account of design and intelligence, and a few lessons, when the fancy is warm, how to explain and how we should wonder; or, after similar professions in the titles of others, we are presented with only a curious display of the art of logic. To a fact or two we see numerous chains of reasoning appended. On these chains are hanging important and general conclusions; and these conclusions afterwards uniting, suspend an elaborate borate system of pathology. The whole has a wonderfully specious appearance; but upon applying the touchstone of experiment, the system falls, the conclusions turn out to be false, the chains are found connected with the fact by only a conjecture or some popular opinion of the time; most of their links are creations of fancy, and their joinings such logical associations as have no analogy or prototype in nature.
Instead of logic, however, a pompous parade of mathematical learning has been sometimes introduced. This has always an imposing aspect, and its presence here may require to be examined with some care. It must be allowed, that it would have indeed been rather surprising if logic and metaphysics had been employed, and mathematics carrying science in their name had not been thought of. Their character had always been deservedly high; and there was scarcely a department of knowledge to which they had not in some respect contributed their aid: their researches, too, had not been confined to mere number and quantity alone; they had explained the momentum of bodies, and all those motions which arise from percussion and gravitation; they had ascertained the distance of the stars, the velocity, magnitude, and orbits of the planets; they had accounted for the phases of the moon, the phenomena of eclipses, and return of comets; and bringing their knowledge from the heavens to the earth, they had shown the causes of the days and nights, of the years and the seasons, in all their varieties throughout the globe: they had taught the chronologer how to dispose of the periods of time, and how he might best assist the historian to arrange his events: they had pointed out the origin of tides; had informed the mariner how to direct his course through the ocean; and had taught the geographer how to describe the regions of the earth, and assist the traveller in his laudable pursuits after knowledge and science: they, in short, had unfolded the wonders of mechanism; and, diffusing light over every branch of that philosophy which is called mechanical, and has long been dignified with the name of natural, had afforded the finest specimens of reasoning with which the human mind is acquainted.
A science of such distinguished utility could hardly fail to excite the admiration of all who knew it, or even had heard of it. And at a period when it was fashionable, it was scarcely possible for the physiologist to pass it unnoticed: the truth is, he very soon discovered its excellency. Bellini of Florence first introduced it; and it was at last so warped with physiology, that there were some who could hardly conceive a physiology existing without it. The justly celebrated Professor Borelli, one of its most enthusiastic admirers, employed it so well in showing how the muscles acted as ropes and the bones as levers, that he thence explained with the happiest effect the phenomena of standing, of walking, of leaping, of flying, and of swimming, in different animals: this task he performed in the first part of his famous work *De Motu Animalium*. But, wishing to know more of the animal economy, and feeling himself inspired with new hopes, he ventured in the second to explain also in the same way the interior motions and their proximate causes on the principles of mechanism: he there gives a minute account of the motion of the muscles, of the heart and its pulsation, of the circulating blood, of the office of the lungs, the kidneys, and the liver, of the nervous fluid and the seminal secretion; of vegetation, generation, nutrition, of hunger and thirst, of pain, of latitude, and the heat of fever.
Mathematics by him were considered as almost universal interpreters; for except the mechanical he seemed to acknowledge no other secondary powers in nature. He thought, with Plato, that God Himself was always geometrising; and was fully persuaded that physical knowledge could not be acquired but through the medium of geometrical demonstrations and forms. These opinions had begun to be general, when his learned work was published at Rome in the year 1676; and they were no unequivocal symptoms that the reigning philosophy of that time was now in the last stage of decay.
Still, however, as the spirit of that philosophy was not wholly extinguished, physiology continued to be much infested with its metaphysical and logical disputes, and with its physical doctrines of forms of particular ferments, its antipathies, sympathies, its occult qualities, and subtle atoms.
For these reasons, in his inaugural dissertation at Leyden, delivered in the year 1697, the learned Pitcairn expressed a wish that medicine were made a distinct science; that it were established on mechanical principles, on fewer postulates, and more data; and that it were supported by a clear train of mathematical reasoning, which would defy the attacks of the sophist, and which would not be liable to the fluctuations of opinion and prejudice. These sentiments were warmly supported by the great Boerhaave, who, in his aphorisms, has founded his reasonings on the structure of the parts and the laws of mechanics, and to whom an edition of Borelli was dedicated in 1710.
Pitcairn, however, was not content with barely expressing his wishes. Seeing with regret that the state of medicine could never be improved as long as it was connected with the philosophy which was then in fashion, he seemed anxious to effect a separation; and for such a step he wished to have only some plausible pretext. This abused pretext was not long wanting; and was, to be sure, one of the most whimsical that could well have presented itself to his fancy. It occurred to him that the study of medicine was prior to philosophy; that it had begun its course with astronomy, at the time when diseases were supposed the consequence of offended Deity; that all along, as it had shared the fate of astronomy, and had equally suffered in the common disgrace of judicial astrology, it was highly reasonable, in his opinion, that it should still follow the fate of its friend; that it should be established on similar principles, and should be demonstrated by that reasoning which might experience the shock of ages without being moved. So attached was he to the geometrical mode of demonstration, that in his dissertations he appeared to consider it as indeed the only species of evidence, excepting the senses, that could be relied on. But here he was certainly venturing too far; so rash an opinion, and one which, had he previously consulted with prudence, might have been suppressed, was fatal to his cause. We must therefore date the commencement of those attacks to which his system was afterwards exposed. Such an indiscreet species of pedantry was but ill calculated to procure a generally favourable reception for a book with so extraordinary a title as the *Physico-mathematical* mathematical Elements of Medicine. Many learned and ingenious men, the greater part of whose knowledge had depended chiefly on the evidence of testimony, were now disposed to examine, with a steady and awakened eye, his boasted demonstrations. The consequence was that which might have been expected: the result of their inquiries was wholly inauspicious to those new applications of geometry; they found that his facts and experiments were few, that his postulates were endless, and that no mathematical reasoning whatever could extract truth from a false hypothesis, or could fairly deduce a general conclusion from particular premises. The Doctor, they observed, had imposed upon himself, in imagining that either certainty or truth was naturally inherent in any mere geometrical forms; these forms, they said, had been often abused! Plato had thought them somewhat divine; the superstitious had employed them as charms; Pythagoras had made them the symbols of his creed; and even in the writings of the learned Professor himself they frequently served no other purpose but to give an air of importance to trifles; to bestow on error the appearance of science; and to give a simple and a trite remark the look of research, and of acute and profound erudition.
It is unnecessary to recall here the satirical wit, or more properly the scurrilous abuse, with which this system and its author were treated. The mechanic physiology has now sunk into such contempt, that the most illiterate affect to smile at the mention of its name; they seem to forget, or, what is more probable, they never knew, that it once was honoured with the great names of Borelli, Boerhaave, and Newton; and their reading perhaps cannot inform them that it was a noble step to improvement; that it explained the structure of the eye, the movement of the bone, and force of the muscle, and that it may yet perhaps be the means of many interesting discoveries in the living body: discoveries, however, which Heaven will reserve for other minds than those which it makes merely to receive the impressions of the day.
A frequent mistake into which the mechanical philosophers had fallen, was their hopes of being able to account for digestion by the muscular force and action of the stomach. The more they reasoned from this supposition, the more widely they wandered from the truth. A thought of Vallinieri, that in acting mechanically, the stomach was as liable to be affected as its contents, gave a hint to Resumur. On this hint he began immediately a set of experiments; and from a number that were clear and decisive, concluded that digestion was performed by a solvent. Here was a fair introduction to chemistry; the action of solvents was never yet satisfactorily explained by mechanic powers. A new era therefore commences; and chemistry now, in physiological investigations, holds that place which was formerly possessed by geometry and mechanics.
Nor is chemistry undeserving of this rank. From a small beginning, and from modestly professing to observe merely the different phenomena which are the effects of heat and of mixture, it has risen like astronomy to the first eminence among the sciences. By its numerous researches it has found widely diffused over nature a variety of singularly active bodies, which are called salts. Of these salts it has noticed some which change a blue vegetable tincture into green, and others which change that tincture into red: the former of these it has called alkalis, and the latter are known by the name of acids. It has observed, that when acids and alkalis are brought into contact, and either of them nearly in a fluid state, they encounter with violence, effervescence and heat, and form a salt, which being neither acid nor alkaline, is called neutral. It has been remarked that all these salts, whether volatile or fixed, whether fluid or concrete, have each permanently uniform characters; and that, though sometimes blended in a mixture, or made to evaporate in a solution, yet when they are separated they resume their taste, their smell, their colour, and their form, and exhibit, as before, the same power in dissolving earths, metals, and stones, and in making inflammable bodies to smoke, to kindle and explode with a loud noise. All, however, act not alike upon all bodies; those acids which dissolve iron remain quite harmless upon gold. And chemistry here has been led to observe that particular salts show a preference for particular bodies, that there is in them an appearance of choice, and that their character is never to be known but by studying their different elective attractions.
Besides salts, chemistry of late has also discovered a number of bodies that are far more wonderful, full more active, and some of them at least still more widely diffused over nature. These are certain aeriform fluids which are called gases: these gases, like the mind itself, are discernible only by their effects; all are elastic, and all are combined with the principle of heat. Their kinds are various; some are inflammable, some are saline and soluble in water, some are neither the one nor the other, and some distinguished by the name of air, maintaining combustion and respiration: their importance is such that there is not a single process in chemistry, nor perhaps one regular process in nature, "in which the phenomena of the disengagement or fixation of heat, and the disengagement or fixation of elastic fluids, are not observed either separately or together." Two of these fluids compose water, two the nitric acid, two ammonia, and three of them are found in atmospheric air; one of them is thought, with a good deal of reason, to be the alkaligenous principle in bodies, and two of them to be the constituents of oil: the principle of acidity is already known to be one of the two which compose water. The same fluid oxidizes metals, supports flame during combustion, communicates heat to the circulating blood, and maintains life in the act of respiration.
By that knowledge which it thus has acquired of salts and of gases, by its more ingenious modes of analysis, and by some discoveries which it has made concerning the nature of heat and of light, chemistry is now able to account for many phenomena that before were inexplicable. In France particularly it has been recently extending its researches with a good deal of ardour towards the phenomena of both the animal and vegetable kingdoms: it has there found its salt and its gases, its heat, and its light, active and lively.
It is more than a century since it observed that plants received their nourishment by pure water and atmospheric air; of plants that from these alone they derived their extracts, their mucilage, their oil, their coal, their acids, their alkalis, and aroma. But since the discovery of different kinds of elastic fluids, it has farther remarked that they grow rapidly in hydrogenous gas (a), and in air mixed with carbonic acid; that affixed by light their leaves absorb hydrogene from water, carbone from the acid of which they are fond; and thus decomposing the one and the other, disengage from both the oxygenous principle or vital air, and restore to the atmosphere salubrity and health.
Leaving vegetables, which, by analysis in close vessels and in red-hot pipes, it has reduced to hydrogene, oxigene, azote, and charcoal, it has made discoveries no less important in the animal kingdom. It has found that the food of the nobler animals, which immediately or remotely is prepared by vegetables, is generally acted upon by a solvent: it has proved by experiment that the animal organs can fix azote; can decompose atmospheric air; can form lime, iron, and carbonic acid, as well as vegetables, produce a number of saline substances, which no art could detect in their food. Nor is it here that such discoveries are meant to terminate; these seemingly creative powers of vegetation and of animalization, with other phenomena in the structure and economy of living bodies, chemistry imagines that it will yet be able to explain. We may safely venture, however, to predict that something more than its present knowledge of the various effects of heat and of mixture will in this case be found necessary to ensure success. The late discovery of elastic fluids and their singular properties afford the strongest reasons to suspect that we yet may be ignorant of many agents which nature employs in the functions of bodies. But whatever be the truth, we are almost certain that these agents discovered by the chemists are not alone concerned. Electricity, and magnetism, and what have been called animal electricity and animal magnetism, must not be excluded from acting some part. The growth of plants, it is well known, is considerably affected by the electrical state of the atmosphere; it is sensibly promoted by a proper use of the vegeto-electrometer, and has been said to indicate a difference between the negative and positive electricities, whether these be kinds or states of the fluid. Such too is our present knowledge, that electricity as yet seems the only cause to which we can ascribe the seeming chemical affinities of the dew; its constant practice in avoiding some bodies, its predilection for others, and particularly its attachment to the living points of plants and of leaves: nor is this electricity wholly unconnected with the animal kingdom; when we think of its singular fondness for points, it occurs that one intention of our hairs may probably have been to collect and diffuse it. It is plainly excited in cross rubbing the hair of some animals, and when we wear silk, it is frequently accumulated upon the surface of our own bodies.
The iron found in plants and in animals is certainly somewhat of a striking circumstance, and cannot be denied to be one reason why magnetism should not be wholly overlooked.
As for animal electricity, or what has been called animal electricity, so, it is now, we believe, generally allowed to hold an important place in the system. It is very perceptible in all those nerves which are subservient to voluntary motions; nor is it limited to these alone. In several instances where metals were applied to the nerves of the heart, which nature has destined to spontaneous motions, they were seen to awaken the dormant powers in the muscular fibres of that viscus. We here speak only of the nerves; but the Torpedo, the Gymnotus electricus, and Silurus electricus, possess a particular structure of organs for collecting this fluid, for discharging it at pleasure, and for giving a shock. If those who are accustomed to the common kind of electrical experiments, may at first be surprised that this electric fluid in the animal is not discharged from the nerves by water, or any other metallic conductor that is pure and unmixed, another fact, which is fully as striking, though it has not been hitherto mentioned by any observer known to us, appears to merit equal attention: Cut away the leg of a frog, uncover a part of the crural nerve, place the limb now on a table on which an electrifying machine is working, you will see the muscles strongly convulsed at every spark which you draw from the conductor, but remaining motionless upon the discharge of the Leyden phial.
Animal electricity naturally suggests animal magnetism. This last has been productive of more wonders magnetism in the human frame than all the preceding agents together. Under the management of Mesmer at Paris, and his pupil Delon, it filled all who observed its effects with surprise and astonishment. It seemed to unhinge the powers of the mind, and affect the whole animal economy; it excited the most extraordinary emotions; it raised and allayed the different passions; it changed aversion into love, and love into aversion; it created pain, it healed wounds, and cured diseases as if by enchantment.
These discoveries were made by a quack, who knew not the cause by which he produced so singular appearances. The celebrated Franklin, who first supposed that the electrical fluid was the thunder, was placed at the head of those gentlemen who demonstrated that this species of magnetism was the same power that had long been known under the name of imagination.
This last discovery, if the blushing pride of modern philosophy could but stoop to improve an important hint, though originally suggested by an empiric, might greatly enlarge our knowledge of mind, and explain some things in the animal economy which appear yet to require a solution. At any rate, it sufficiently proves that the influence of mind is very extensive in the higher parts of animal creation. Many facts would argue that it increases as we rise in the scale: but the sole intention here was to show, that chemical agents are neither almighty nor everywhere present; that in the internal organic economy of living bodies they act but a part; and that, like the other agents in nature, they are obliged to confine their operations within those limits which the great Author of being has prescribed.
The aid which anatomy affords to physiology is now to be considered. Physiology in general and the anatomy in study physiology.
(a) Hydrogenous gas acts with more energy than any other substance in dissolving carbones; it mixes with carbonic acid and with azote, and sometimes holds in solution sulphur and phosphorus. See Fourcroy's Dif- study of anatomy are so closely connected, that, as Haller imagined, they can hardly be separated even in idea. In his opinion, the man who should attempt to become a physiologist without anatomy, would act as wisely as the mathematician who, without seeing the wheels or the pinions, or without knowing the size, the proportions, or the materials of any machine, would yet presume from mere calculation to determine its powers, its properties, and uses. In this comparison, the importance of anatomy, we are really persuaded, is not represented in a light too strong; nor does that medium through which it has been viewed appear to have magnified beyond nature.
Whether art or science, anatomy is one of those eminent accomplishments without which no one is able to prosecute his studies with half that pleasure and success which he might in either the animal or vegetable kingdoms. Having been always accustomed to assign it one of the highest and most honourable places among those branches of human knowledge which are styled liberal, we must be excused if we dwell a little in exposing an attempt to convert it to a craft.
It is with surprise, and a mixture of regret, that we see a writer of distinguished merit wishing thus to degrade it, and seeking to confine it as well as physiology to that profession which chanced to be his own. The dignity of a science, which he considered as his glory and his pride, should have certainly extinguished in a generous mind the low and discrediting policy of his trade. It is indeed with reason that he thinks it unfortunate, "that those who, from the nature of their education, are best qualified to investigate the intricacies, and improve our knowledge of the animal economy, are compelled to get their living by the practice of a profession which is constant employment." We lament the misfortune as much as he can; but we reason not from it in the same way. Instead of complaining that "idle profession-men," particularly "of the church, should become philosophers and physiologists as it were instinctively," we are happy to learn that men of enlightened and cultivated minds are thus so readily disposed to enlist us; that nature conducts them as it were by instinct; and that happily they enjoy all that leisure which is deemed so necessary for such an undertaking. The genius of some, and the liberal education which they all must have had opportunities of acquiring, by no means impress us with any unfavourable ideas of their aid.
Our author allows them to look through microscopes and examine the red globules of the blood: They may too, he says, view animalculæ, and give us a candid relation of what they see; but should not presume to carry their reasoning into a science of which they can know nothing, or hope to throw light on a subject which it is impossible they can understand. But, to speak freely, after considering the great physiological discovery of Priestley with respect to respiration, the most important probably, not even excepting that of the system of absorbents, that the science has witnessed in the present age, we see no grounds for prescribing such laws or fixing such limits: and although he may treat the illustrious Reaumur and Abbé Spallanzani as nothing more than makers of experiments, and declare a resolution to place no confidence in those which are made by gentlemen and priests; he will not certainly deny that others have as well as he a just right to think for themselves.
Were such sentiments to become universal, it is difficult to say what would be the consequence. In this country, the law and the church require from their members a formal certificate, that, besides the professional, they have also attended some literary classes at the university. To our medical classes boys are admitted from the shop and from the school, and may afterwards pass the two colleges of surgeons and physicians, by exhibiting a little skill in their art, or at least by paying the stated fees. On these accounts, being anxious already for the fate of a profession which we respect, and considering the degeneracy to which it is exposed, not we hope the degeneracy into which it is sinking, we should be sorry to see it deprived of that respectability which it may derive from the countenance of men professing general literature and science.
It is very true, that gentlemen and priests may not be anatomists; and not a few anatomical disputes might seem to intimate, that persons may be very eminent anatomists without being either gentlemen or priests. Still, however, there is nothing incompatible in those characters; and, were we to judge from their writings, it was certainly a thing of which Bacon, Newton, and Locke never dreamed, that the study of the priest, or the mere circumstance of being a gentleman, was to blunt their acuteness for physical research, or in after times to affect their reputation as men of genius.
"When men have begun to reason correctly (says Dr Hunter), and to exercise their own judgment upon their observations, there must be an end to delusions. Many doctrines of old physicians and of old women will meet with proper contempt; the tyranny of empty pomp and mystery of physic will be driven out of the land, and forced to seek shelter among less cultivated societies of men."
If the learned professions wish to be respected, let them respect each other: for our part, we esteem them all: and whatever assistance either they or others may afford to physiology, they may be assured that they will not find us anywise disposed to detract from its merit. Divested of prejudice, we value as highly the discovery of Priestley, which explains respiration, as if it had come from Albinius or Haller; and with as much readiness acknowledge obligations to the celebrated painter Leonardo da Vinci, as if he had been a doctor of physic. See Anatomy, p. 667.
But while we are thus impartial to others, we would not be unjust to professional anatomists. Their learning, hours and ing, their patience, and ardour, have been great; and candour obliges us to assert their claim to the most numerous and important discoveries that have yet been made in physiological science. The pains which they have taken, the prejudices which they have surmounted, and those feelings which they have sacrificed in describing the parts of the dead body, place their labours beyond all praise.
But their discoveries have not been confined to a mere knowledge and description of parts. In the still fabric, just as in a time-piece or a broken mirror without motion, the whole presents a very confused and even an uninteresting appearance. In this case, should the man of reflection happen to ask, where are the organs of the different functions? all would be silence, and nothing would be found to make a reply to such an inquiry. The arterial system is relaxed and empty; the muscular fibre cannot be roused; the heart has ceased from its wonted beatings; and the nerve refuses to convey sensations. On this scene the eye of the anatomist could not be expected to dwell long with much satisfaction. Curiosity would induce him to look beyond it, and study the design. He would soon perceive, that to know the uses of the several parts, they must be seen alive and in action. But here new difficulties would arise, and feelings of compassion would exclaim against any farther pursuit. The natural zeal, however, of inquiry, the good of mankind, and the love of science in a generous mind, are not easily resisted.
To his lasting praise, and the singular improvement of true physiology, the anatomist has examined the living body, and has there observed, that all motion proceed immediately from the muscular fibre; that the muscular fibre again derives its power from the nerve, which terminates in the brain; that fibre, and nerve, and the whole system, are nourished by the blood which comes from the heart; and that the waste of blood is supplied by the lacteals, which absorb nutritious matter from the food as it passes along the intestinal canal.
He has also observed, that the blood, which is in continual motion, has a circular course; that other vessels along with the lacteals are employed to absorb; and by means of injection has shown the route of the different fluids as clearly in the dead as they could have been seen in the living subject.
When his eyes have failed in tracing objects that were too minute for unaided sight, he has called in the help of the microscope, and discovered the red globules of the blood, animalcule in the semen, and the amoebos of the arteries and veins; and when the microscope could lead him no farther, he has had recourse to chemical analysis, and made discoveries equally important in demonstrating the bodies which compose the several fluids and the solids.
Besides these services which the anatomist has rendered to physiology, the science is likewise greatly indebted to him for those various and ingenious methods which he has taken to diffuse his knowledge. Whatever has occurred remarkable or rare, he has studied to preserve either dried or in fluids that resist putrefaction. By corroding the parts which he has injected in a certain acid, he has given an idea of the vascular system, which is at once instructive and elegant. Where it has been necessary to destroy the parts when incapable of preservation, or where the preservation would have been expensive, he has not neglected to represent them in models of wax, or to perpetuate them in accurate casts of lead or of tinco: and, lastly, that the valuable fruits of his labours might not be confined in his room of preparations or to his pupils, he has described most of them in drawings, has multiplied his drawings by correct engravings; he has even published his numerous engravings, and to render them intelligible, has illustrated each with copious explanations.
From this account it might be supposed that the anatomist has done all that can be reasonably expected from him. If drew, however, such a conclusion, we might certainly be charged with precipitation. His views have hitherto been too confined, nor have they been directed with all that skill which a rational and comprehensive physiology would require. Preliminary observations. As if chiefly guided by the rant of the poet, that "the noblest study of mankind is man," he has cultivated his art principally with an eye to medicine and surgery; and while he has dissected the human body with a tedious minuteness, he has seldom looked into those of brutes but when he has wished to illustrate a theory or establish a hypothesis.
As some apology for such a conduct, there is indeed but little immediate or pecuniary advantage to be derived from comparative anatomy; and those who have heard of the fox and the grapes will readily perceive, that few will be disposed to commend a science which reflects not much credit on their knowledge, and which they are led from sentiments of pride to treat as either contemptible or useless. The decisive tone and affected air of superior discernment being not unusually a very tender part of the character, they often form that mark of distinction which is seldom resigned but with the utmost degree of reluctance. It is, however, allowed, that any opposition from these causes ought not to frighten an aspiring genius. His nobler mind should look beyond pecuniary prospects; and he ought to have fortitude enough to despise the sneers and malice of pompous ignorance. The other difficulties which he has to encounter in his own estimation may not be so small.
In seeking to enlarge the field of inquiry, he will soon experience that he wants a language, or at least of a nomenclature fitted to express the different objects which must necessarily occur in his researches. He will find too that he wants those proper classifications of the animal kingdom, which are equally necessary both to abridge and direct his labours.
The first nomenclature of the anatomist was formed upon the dissection of brutes; and most of its terms, the anatomists rete mirabile, are now useless, or ten to mislead medical men who employ them in their dissections of the human body. The few of its parts which still are retained, as the different names and divisions of the gut, are much more applicable to the usual appearances in certain quadrupeds, than to any thing which we meet with in man.
This first nomenclature declined with the studies which gave it birth, and with the decline of that superstition which permitted no other studies of the kind. Since the days of Vesalius the human body has been chiefly dissected; and the nomenclature which has thence arisen, and has since been assuming the form of a language, if adapted at all, is peculiarly adapted to that subject. Were we now therefore disposed to examine the internal economy of animals in general, we should see at once that the present nomenclature is as ill suited to comparative anatomy as the former nomenclature was to the dissection of the human body. The several facts which confirm this assertion are but too numerous. To give one or two: In a late work, The Physiology of Fisher, the celebrated author is obliged to inform his reader in a note, that when he makes use of the following terms, superior, inferior, anterior, and posterior, the fish is supposed to be standing erect in the attitude of man; and in his ingenious Contemplation on Nature, Bonnet, besides the absurd practice of calling nerve by the name of marrow, has been pleased to observe, that in certain insects the spinal mar- row is not in the spine, but in the opposite side of the body, running longitudinally along the breast.
Applying occasionally this nomenclature to the small number of birds and quadrupeds which we have dissected, it was much strained with respect to their skeletons. Even forced analogy could not bring it to explain many distributions of the nerves and blood vessels; and when it was employed in naming the muscles, in most cases it turned out to be useless or absurd.
We were first led to observe its defects on hearing of the names of bones of the pelvis, called the os ilium, the os ischium, and the os pubis, united behind by an os sacrum, which is tipped with a coccyx or bone of a cuckow: we thought it likewise somewhat remarkable to find a goat, a boat, and a conch shell, among the external parts of the ear; and within the tympanum a hammer and its shaft, a fishy, a stirrup, and a periwinkle. But these defects were most seriously felt in raising the different muscles of a dog, and comparing them generally with Albinius's tables. These tables and muscles, to our great surprize, did not reflect that mutual light upon one another which we expected. To obtain here more accurate ideas we got the comparative myography of Douglas. At one glance the etymological table of this work demonstrated the confusion and the imperfection of the nomenclature. In his, as in other books of myography, the muscles are explained by describing their origins, insertions, and uses: but the table shows, that their names are never, excepting only in a few cases, derived from any of these three circumstances, which in every description are uniformly noticed in all muscles. Their names on the contrary are frequently taken from their particular form and appearance in the human body, or from those circumstances which are constantly varying in every animal; just as if muscles of the same origin, insertion, and use, should in all animals have a similar colour, a similar mode of insertion and origin, a similar composition and variety of parts, a similar course and direction of fibres, a similar figure and shape, a similar passage through certain places, a similar proportion with respect to one another, or should be formed of a similar substance.
If we pass to the membranes, as expressed in this nomenclature, we shall not discover that their names are more philosophical. A periosteum covers the bones, a pericranium the skull; the cavity of the thorax is lined with a pleura, that of the abdomen with a peritoneum; and what is surely somewhat remarkable, bones which are hollow have a periosteum on their inside: the membranes in the skull are by way of distinction denominated mothers; the one which lies next to the cranium is the dura mater or hard-hearted mother, while that which immediately enwraps the brain is the mater pia or the affectionate mother.
Of all the terms, however, that occur, the cavity of the skull contains the most extraordinary collection: we there meet with a Turkish saddle and with the feet of a fer-horse, with a ring, with a lyre, with a sickle, with a bridge, with a writing pen, and a wine-prefs. A few of these names belong to the substance of the brain itself: where one part is called from its hardness the callous body, another from some fancied analogy the medullary substance, and a third from being on the outside is named the cortex, and from its colour the cineritious. These are not all: there are besides footstalks of the cerebrum and cerebellum; the thighs and arms and fore and hind legs of a grand division, the medulla oblongata; there is also a vault and two or three pillars, one pair of fluted bodies, two beds, and a couple of horns; some cavities which, from a supposed resemblance to stomachs, are called ventricles choroid coats; two bodies, named from the olive, two from a pyramid, and one from a rine, which is chiefly remarkable for having once been thought the residence of the soul. At some distance in the cerebellum we are however pleased to meet with a name that is somewhat elegant, the tree of life. In this there is a degree of refinement, which must strike one as it comes unexpectedly. The following names are in the lowest style of obscenity: they are wormlike and mammillary protocoles, they are nates, testes, an anus, and a vulva; which, in order to save the blushes of our readers, we shall leave in the language in which they were conceived. A singular part is placed immediately under a funnel, and is named from its use the pituitary gland; it was meant originally to secrete a phlegm, but it holds that office now as a sinecure (n).
Ridiculous and whimsical as many of these appellations are, they generally have some allusion to their subject, and are by no means the most exceptionable in this nomenclature. The names of discoverers which have been imposed upon various parts, contain no description at all; and the only purpose which they can serve is not to promote the interest of science, but to immortalize the anatomists. As many of these have not been more than insensible to fame, they or their friends have taken the freedom to introduce parts to our notice, not by telling us what is their nature, but by demonstrating who was the first that observed them. Upon reading therefore the catalogue of names that occur in anatomy, one would imagine that many of these ingenious discoverers had supposed themselves not the discoverers but the inventors of several parts in the animal economy. In our vascular system is the ring of Willis, the vein of Galen, and the large wine-prefs of Herophilus. We have in our brain the bridge of Varolius; and in our nerves we possess the property of various discoverers. The holes of Vidius, and the caverns of Highmore, are in our bones; some small muscles in the sole of our foot is the fleshy mass of Jacobus Sylvius; a part of our eye is the membrane of Ruysh; and in those cases where they are to be found, Cooper lays claim to particular glands; two canals from our mouth to our ears are the tubes of Eustachius;
(b) That our readers may judge whether or not these names be fairly translated, we subjoin the originals here in a note. In the ear, tragus, scapha, concha, malleus, incus, flaps, cochlea; in the cavity of the skull, sella Turcica, pedes hippocampi, annulus Willisii, psallodae vel tyra, falsa dura matris, pons Varolii, calamus scriptorius, torcular Herophili, corpus callosum, subtantia medullaris, subtantia corticalis vel cinerea, pedunculi cerebri et cerebelli, femora, brachia, crura anteriora et posteriorea medulla oblongata, formix, corpora striata, thalami nervorum opticorum, cornua nervorum opticorum, corpora olivaria, corpora pyramidalia, glandula pinealis, arbor vitae, tubercula mamillaria, appendices vermiformes.
The man who will readily observe the defects of this nomenclature is not he who has learned it already, and who no longer is acquiring his ideas through its imperfect and confused medium; nor is it he whose studies are confined to the human body, the particular subject on which it was formed: He who will sensibly feel its inconvenience is the young anatomist, who must receive his knowledge through its channel, commit its vocables to his memory, and use them afterwards in recalling his ideas. Another who must soon perceive its failings, is he who engages in comparative anatomy, and who is anxious to extend his views beyond that which the foolish indolence of conceited bombast has called the microcosm. A third will be he who has remarked the numerous synonyms which different authors have thought themselves warranted to substitute in place of the old terms: for these repeated attempts at amendment are a strong proof of that estimation in which it is held by the anatomical writers in general: And, lastly, that man cannot hesitate long to pass upon it a condemnatory sentence, who, like Wilkins, Locke, Condillac, and Reid, is a person of extensive and profound reflection, who is well acquainted with the intimate connection between accurate expressions and accurate ideas; who knows how much the improvements of language are able to facilitate the progress of science; or who has experienced the wondrous effects that have already resulted from the example and labours of Linnæus, and particularly from the new nomenclature in chemistry, which can hardly be too much valued and admired.
Our intention here is not to suggest a particular plan for any new anatomical nomenclature: the state of our knowledge may in this respect be yet too imperfect, and perhaps it may be necessary to see more of the animal economy, before we should venture on such an undertaking. We may however, in general, observe, that this nomenclature, like the languages of nations, ought not to be formed with any view to an individual, a species, or genus; and after that be carelessly extended by fanciful analogies to new objects, and from these again be extended to others; thus making metaphor to spring out of metaphor without end, until the original figure be lost, and revived and lost again, times without number. It ought to contain as many as possible of those terms which, understood in their primary sense, might apply to the whole animal kingdom and living bodies, without any metaphorical expressions, if, in describing the tares and colours, such expressions can be avoided. Instead of the words anterior, posterior, inferior, and superior, which are perpetually shifting their meaning with a change of attitude, it ought to have words of one constant invariable import, expressing the regions of the head and the back and their two opposites. These terms, with right and left, would be found in anatomy to answer nearly the same purpose that the degrees of longitude and latitude, or the points of the compass, do in geography. Every part would then be considered as lying within or as pointing to six different regions, the right, the left, the head, the back, and their two opposites. If more particular descriptions were wanted, the definitive terms might then be taken from the more immediately surrounding parts; thus giving an account of the ethmoid bone, D'Azyr borrows the definitive words from the regions of the cranium, the frontal, basilar, facial, and occipital; or from the regions in immediate contact, the cerebral, palatine, nasal, and sphenoidal.
If an object attainable, this nomenclature too should be derived from one origin, and not like the present be a wild incoherent Babylonish gibberish of a number of mixtures. It ought to aim at conveying its ideas with clearness and precision, and yet fully, concisely, and promptly. In point of simplicity it ought to study the ease of the memory in receiving, retaining, and in recollecting. To prevent a needless multiplicity of terms, it ought to avoid puerile minutiae, which serve no end but to render description tedious and confused; it ought to avoid such trivial divisions, as those of the gut into duodenum, jejunum, ileum; or those of the artery into subclavian, axillary, brachial; and, lastly, it ought to be formed on a plan containing certain rules of construction for giving names not only to parts already discovered, but to those parts which are still unknown, or which distinguish individual and species.
In imposing names, it might perhaps be of some advantage to examine not only together, but separately, the great constituent parts of the system; as the bones, the ligaments, the cartilages, the muscles, the membranes, and the glands; the nervous, the fangiferous, and absorbent systems; and all these with their properties and uses periphrastically arranged. How far a regularity in composition, and a uniform variety of terminations, might be of use in this nomenclature, can best be conjectured from their great importance in the new philosophical language of chemistry.
It has been observed, that such a nomenclature, to encourage and assist the comparative anatomist, is still wanting; and it also was remarked, that we yet are unacquainted with proper classifications of animals, peculiarly fitted to direct and abridge the anatomist's labour, and to satisfy the inquiries of the physiologist.
Our present physiological arrangements are, like our The pre-nomenclature, principally suited to the human body. To take our instance from the celebrated Haller, he begins his Outlines with the simple fibre, and the cellular texture, of which he is anxious to compose as fine as many of the solids as he can. He then proceeds to more of the organs, describing with great erudition and care their different uses and structure in man. These organs, however, which he describes, and those analogous with respect to their structure, are confined to a part of the animal creation. As different classes of the animal kingdom have with similar functions various varieties of organs, and as one function is consequently performed in different ways, it is evident that organs the function not to form the general divisions in any physiological system of arrangement, because we should then confine to have a new arrangement for every new species of organs. Of this truth Haller and others have not been ignorant. They have also divided their subject into functions; functions; but all they are functions in the manner performed by the human body. This body has engrossed so much of physiology, that we often see the functions explained with scarcely any allusion to their organs; as these are supposed to be always the same, and already known from the usual directions.
Haller's physiology is professedly that of the human body. His conduct here was seemingly the effect of general custom; it did not arise from any contempt of comparative anatomy. There have been few who esteemed it so highly, who have studied it more, or applied it so skilfully. He declares there are many parts of our bodies whose functions can never be fully explained, unless we examine their structure in quadrupeds, in birds, in fishes, and even in insects; though he therefore had dissected of human subjects to the number of 350, yet the number which he dissected of brutes, and, what is more, dissected alive, was much greater. Numerous, however, as were his dissections, they were too confined for general physiology. That requires a range more extensive; and, to shorten the labour, different classifications of animals from any of those to be usually met with. This assertion hardly needs a proof.
There is nothing more certain, than that were the anatomist to dissect animals as they occur in the system of Linnæus, or any other naturalist, his toil would be immense, and the knowledge which he thence would acquire of functions would scarcely be found to bear to it even the smallest proportion. By this observation we mean not to object to those ingenious classifications which Linnæus and others have employed to facilitate the study of zoology. All their classifications may be useful; and many display that extent and clearness of comprehension, that distinguishing acuteness, and that laudable ardour for the interest of science, which ought to render their authors immortal, and entitle them to the gratitude of future ages. Yet these systems are formed with a view different from that which principally ought to direct the physiologist. They were meant to contain a full enumeration of the objects of zoology so far as known; to exhibit them arranged in different classes and subordinate divisions, according to such obvious and distinct marks as might strike at a glance, or appear on a cursory examination. To him who is entering on the study of zoology, they show at once the extent of his subject; they elevate his mind by the grandeur of the prospect; and when better employed than in pleasing the fancy or in rousing the rapturous feelings of a poet, they draw his attention to those significant and marked signs in which the language of nature is written. They assist his judgment in the art of arrangement, and give to his memory a power of recollection which it had not before. To the natural historian they perform a service equally important, if not essential, to his undertakings: to him they supply the place of chronology; and instruct his readers by the chain of connection which they give to his thoughts, and by that perspicuity which they invariably bestow on his language.
These arrangements, however, with all their advantages, are not the arrangements which the physician between would wish the anatomist to observe in his dissections. They are certainly useful in studying the manners, dispositions, and habits of different animals, and all that part of the outward economy which indicates something of their wisdom and design. But they little illustrate that internal structure on which this outward economy is founded, or tend to explain the more secret functions which, not depending on the will of the creature, only display the power and omniscience of him who made it. This consequence is easily conceived, from considering the difference between zoology and what has been here defined physiology. Zoology is chiefly led to examine the animal kingdom as it usually presents itself to the eye, including a great variety of objects; physiology only that single part of the animal economy which is chiefly made known by anatomy and chemistry. Zoology has been wont to divide its kingdom into so many classes or orders of animals; physiology would naturally divide its economy into so many functions. Zoology has subdivided its classes by certain obvious and exterior marks, as the teeth and the claws; physiology would naturally subdivide its functions by the many varieties of those organs which are destined to perform them, as the different kinds of lungs and of stomachs. Zoology but cursorily mentions the functions as forming a part of the history of animals; physiology takes notice of animals only when they are of use to illustrate its functions. From this comparison it will readily appear, that things which are primary in a zoological will often be secondary in a physiological species of arrangement; and that things which are primary in a physiological will often be no more than secondary objects in a zoological. This is very conspicuously the case in one of the grand divisions of Linnæus into mammalia, where the important secretory organs of the milky fluid are noticed only, like the colour of hair or the length of a tail, as a good outward mark of distinction; and likewise in the excellent table of D'Aubenton, where the function of digestion is not even alluded to at all; although he had complained that there was more of art than of nature in the common arrangements, that classification by outward marks had confounded things of a different structure, and that the lesser divisions should be made only by marks relating to the functions. | ANIMALS | With a Head | The most part without a Head | |---------|-------------|-----------------------------| | Nostrils | Without Nostrils | | | Ears | Without Ears | | | Two Ventricles in the Heart | One Ventricle in the Heart | The Heart variously formed or unknown | | Warm Blood | Blood nearly cold | A whitish Fluid instead of Blood | | Inspiration and Expiration of the Air at short Intervals | Admixture of Air by Gills | No apparent Entrance to admit air | | Viviparous | Without Teats | Oviparous | | With Teats | 6th Order | Fishes | | 1st Order | 2nd Order | 4th Order | | Cetaceous Animals | Birds | Oviparous Quadrupeds | | 5th Order | Serpents | Insects | | 8th Order | Worms | | | Four Feet and hairy Skin | Fins and no Hair | Feathers | | Scales without Feet or Fins | Scales with Fins | Antennae | | Neither Feet nor Scales | | | It is plain from this table, and from what we have mentioned concerning Haller, that it would be injurious to anatomists and naturalists to say they have never paid any attention to the physiological modes of arrangements. It can only be said that they have not paid to them all that attention which they deserve; and that no general physiological system of arrangement, excepting D'Azyr's, has, so far as we know, been yet attempted.
How such an arrangement ought to be made is easily described, though by no means very easily executed. It needs not a proof that functions should form its primary divisions; that its subdivisions should be the varieties of these functions; that the whole should be both distinguished and explained by the kinds and varieties of those organs, by which they are performed; that the descriptions of these organs might partly be collected from the several works of natural historians and comparative anatomists, as from the dissections of the French academy, from numerous fragments of the Curieux de la Nature, from the collections of Blasius and Vallentini, from the writings of Haller, from the works of the celebrated Hunters and Monros, from the publications of Hewton and Cruikshank, and those who have lately been making discoveries in the system of absorbers. D'Azyr has mentioned a great many more. He particularly recommends Perrault, Du Verney, Collins, and D'Aubenton, on Birds and Quadrupeds; Charas, Roefel, and Fontana, on Reptiles; Ray and Willoughby; Ardei, the Gouans, and Broussonet, on Fishes; Swammerdam, Malpighi, and Reaumur, the Geoffroyes, Bonnet, and Lyonnet, on Insects; and, lastly, the curious researches of Willis, Ellis, and Donati; of Trembley, Baker, Baeter, and Boasch; of Forskal, of Adanson, of Muller, Pallas, Spalanzani, and Diquemare, concerning Worms, Zoophytes, and Polypes. Where any errors are to be corrected, or where any deficiencies are to be supplied, it is needless for us to observe that recourse must be had to new examinations and to new dissections, where it may be of some use to attend to the foods of animals, to their places of abode, and their modes of life, as circumstances leading to some internal varieties of structure. To the list of authors we might have added Camper on Fishes; and we should not forget the excellent writings of D'Azyr himself, whose table of physiological arrangement is a work of merit that be-speaks reflection, ingenuity, and labour, and which follows here, with only a small variation in form.
A TABLE of the Functions or Properties of Living Bodies.
1. Digestion. 2. Nutrition. 3. Circulation. 4. Respiration. 5. Secretion. 6. Ossification. 7. Generation. 8. Irritability. 9. Sensibility.
Every body in which one or more of these functions are observed is to be considered as possessing organization and life.
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1. Digestion.
Living Bodies Which have One or more stomachs, easily distinguishable from the oesophagus and intestinal canal,
Man. Quadrupeds. Cetaceous animals. Birds. Crustacean animals. Oviparous quadrupeds. Serpents. Cartilaginous fishes. Fishes properly so called. Insects. Worms. Zoophytes. Plants.
2. Nutrition.
Living Bodies Whole nutritious juices are absorbed By vessels beginning from internal cavities,
Man. Quadrupeds. Cetaceous animals. Birds. Oviparous quadrupeds. Serpents. Cartilaginous fishes. Fishes properly so called. Insects. Crustacean animals. Worms. Plants.
By vessels opening upon the external surface,
3 Circulation.
Having a heart with two ventricles and two auricles, With blood
With one ventricle divided into several cavities and two auricles, With one ventricle and one auricle,
Whose heart is formed of one longitudinal vessel, tuberous and contractile, in which there is a whitish fluid instead of blood,
In which no heart has been yet observed, but only vessels filled with juices of a nature different from that of blood,
Man. Quadrupeds. Cetaceous animals. Birds. Oviparous quadrupeds. Serpents. Cartilaginous fishes. Fishes properly so called. Crustaceous animals. Insects. Worms. In some crustaceous animals there is observed something resembling a heart.
Zoophytes. Plants.
4 Respiration.
By lungs free from all adhesion, and spongy, By lungs free from all adhesion, vesicular, and muscular, By lungs adhering to the ribs, and provided with appendages,
By gills of different forms, By stigmata or holes in different rings, By an opening called trachea, or by external fringes, By tracheae,
In which there have been discovered neither stigmata nor tracheae,
Man. Quadrupeds. Cetaceous animals. Oviparous quadrupeds. Serpents. Birds. Cartilaginous fishes. Fishes properly so called. Crustaceous animals. Insects. Earthworms. Aquatic worms. Plants. Polypes.
5 Secretion.
There are no bodies in which secretions are not carried on.
6 Ossification.
Internal and osseous, Internal and cartilaginous, External and corneous, External and cretaceous, External and ligneous, Which have no skeleton,
Man. Quadrupeds. Cetaceous animals. Birds. Oviparous quadrupeds. Serpents. Fishes properly so called. Cartilaginous fishes. Perfect insects. Lithophytes. Crustaceous animals. Shell-fish. Madrepores. The greatest part of Zoophytes. Plants. Insects in their first state. Worms. Polypes.
7 Generation.
Living Bodies
Which are
Viviparous,
Oviparous, whether the evolution of the eggs takes place within or without the female;
Which propagate by slips,
8 Irritability.
Living Bodies
Which have
A body muscular or contractile,
Muscles covering the skeleton,
A skeleton covering the muscles,
No muscular power; no spontaneous movements,
9 Sensibility.
Living Bodies
Which have
Nerves and brain easily distinguishable from the spinal marrow,
Nerves and brain scarcely distinguishable from the spinal marrow,
In which there have not yet been discovered nerves or brain, or spinal marrow,
The above table, which has its divisions marked by the functions, and their kinds and varieties by the kinds and varieties of those organs by which they are performed, differs considerably from a zoological. Borrowing its several marks of distinction from internal characters, it more clearly demonstrates the difference between the mineral, vegetable, and animal, than any system that attempts to arrange by outward appearances.
No minerals, whatever be their forms or the regularity and beauty of their figures, were ever said to possess any thing like organs of nutrition; and however frequently some may recover their lost shapes, they are never supposed either to produce, or assist in producing, their own kind by generative powers. And no plants, however much may be said of animals that want a nervous system and a heart, and are fixed, without the power of locomotion, to one place; we say no plants, though some may represent a few of the simpler effects of sensation, and others may be free to float through the ocean, were ever said to discover any signs of voracity, to possess any thing resembling a stomach, to distend their body by swallowing their food, to apply their food to the mouths of absorbents opening internally; and when the nutritious juices were extracted, to eject it in cumulo. It has been said that zoophytes present similar phenomena. But what are zoophytes? One half of their name would imply that they are animals, and another half would insinuate that they are plants. D'Aubenton reasons with clearness on this subject. True, says he, the greatest part of them are branched like plants, and like plants are composed of concentric circles. Some have a soft exterior substance which is called bark, and a hard interior which which is called wood. Along their branches, and at their extremities, they put forth vehicles which resemble buds; and when a part falls from the whole, it is sufficient, like a vegetable slip, to produce a zoophyte: but do these appearances prove that they are plants?
If ramifications constitute a plant, then many crystallizations will be plants; the shootings of root on our windows will be plants; the silver tree of Diana a plant; our veins will be plants, our arteries plants; and our very feet which ramify into toes, and our hands into fingers, will have some title to be called plants. The truth is, ramification is not universal in the vegetable kingdom; and although it be general, it is no more peculiar to plants, than swimming is to fishes or flying to birds. If concentric circles constitute a plant, some bones of animals will then be plants, and some minerals must also be plants. The wood and the bark are only two metaphorical expressions, which with equal propriety might have been used of the bone and periosteum. But once suppose the zoophyte a plant, it was natural to carry on the analogy, and certainly necessary to have it provided with wood and bark; though it must be allowed that a cornuous substance is not what we commonly mean by bark, nor an evidently hard calcareous substance what we mean by wood. The small vehicles, except in appearance, have no familiarity to buds or fruits: they are the residences of small polypes, to whom the whole structure has been owing, by whom the whole either is now or has been inhabited, and to whom it answers the same purpose as the shell does to testaceous animals.
After thus endeavouring to point out the boundaries between the mineral, the plant, and the animal (A), before we begin to treat of the functions, we must also take notice of another distinction; the want of which has occasioned much unnecessary trouble, and has given rise to not a few ridiculous disputes. This is the distinction between living bodies and some ingenious contrivances of art, which are called machines. It has not been asserted that any machine can either grow or propagate its kind; that it can assimilate the particles of matter that come in contact; that it is able to repair the injuries which it may suffer; that it can accommodate itself to circumstances, can create heat when the cold is keen, or cold when the heat becomes too violent: yet it has been supposed, from established prejudices, and from the successive evolution of parts in plants and in animals, that there is an analogy between a machine and a living body. The living body has been called a machine; and notwithstanding the acknowledged truth of that observation so often repeated since the days of Hippocrates, That the whole is a circle, that nothing is first and nothing last in the animal economy, we are still talking as if living bodies were nought but machines; we are still reasoning as if their parts had existed in succession, had acted in succession, were combined in succession; we are still seeking for what is prior and what is posterior, for what is derived and what is original in point of structure, as if we were examining a work of art; we speak gravely of the viscera, of the thorax deriving a coat from the membranous pleura, the abdominal viscera from the peritoneum, and the branches of nerves deriving a pair from the dura and pia mater of the head; we argue with people who maintain that fasciae are nervous expansions, and the muscles themselves but nervous productions; and although we be hardly able to conceive how the brain could be nourished without blood thrown from the heart, or the seemingly heart move without the assistance of nerves from the coeval in brain, we are still disputing about which was prior and point of existence; a dispute which will probably terminate as soon as that of the ancients, whether the first eggs were from birds, or the first birds were hatched out of eggs.
These dark and inscrutable mysteries of nature we Functions presume not to explain: they point out almost the form a creative hand, and bring us almost into the immediate cle. presence of that Being by whom we live, move, and exist; and before whom the truly feeling and elevated mind is less disposed to examine than adore. We are only to observe, that from this coeval formation of parts which the microscopic part of anatomy has often distinguished from their evolutions, and from this mutual dependance of organs one on another, we are left at freedom to begin at any part of the circle, and treat of the general properties and functions of living bodies.
We now venture on a rude sketch of the order and manner in which these properties may be explained, and in which the facts in general physiology may be afterwards arranged. Another opportunity may produce something more full and correct. In the present sketch, many imperfections will no doubt be found; we already are able to foresee many from our own inability to treat the subject according to its merit. And perhaps the reader, who is possessed of temper and candour, will impute some to the newness of the plan, and the present infant state of the science.
Without blaming the arrangement of d'Azyr, whose genius and labours we shall always respect, we have been induced to adopt the following, from those reasons with which the reader is now to be acquainted.
Attending minutely to a living body, which already has escaped from the seed, the egg, or membranes of the parent, which is wholly disengaged from the placenta,
(a) It is curious to observe how careless we are in annexing precise ideas to our words. Bonnet supposes that in some world more perfect than ours, the rocks may be organized, plants may feel, brutes may reason, and men may be angels. In this passage the form was all that seems to have entered into his idea of the man and the brute; and so new was his notion of a perfect world, that one who believed in the metempsychosis, would naturally imagine that he here had been fancying a state for the damned, where angry Heaven was to fetter the angel in the form of a man, a man in that of a brute, a brute in that of a vegetable, and a vegetable in that of an uncouth rock. How much to be pitied would the creatures be that reasoned and felt, and were at the same time more incapable of moving than an oyster or a limpet! placenta, and depends for the future on the operations of its own organs (b), we may observe, that in order to live, it must be allowed the free use of air, as applied by the organs of—Respiration.
That, in order to grow, it must have likewise a supply of food, which is a substance somehow adapted to its constitution; and which, on being received into the system, is
Prepared by—Digestion, Taken up by—Absorption, Distributed by—Circulation, Assimilated by—Nutrition, And the whole carried on by means of—Secretion.
We next may observe, that in order to enjoy the free exercise of these functions, it must be secured from the more common and external injuries of its situation; and that this is done by certain integuments originally produced, and when it is necessary, afterwards renewed by that function; which, till we receive a new nomenclature, we shall venture to call by what may be rather an uncouth word—Integumentation.
We again may perceive, that these functions are all dependant on a general principle—Irritability:
By which the system is rendered by stimulants susceptible of—Motion;
Accommodates itself to different circumstances by means of—Habit;
Alters its shape by successive—Transformation;
Produces the species by—Generation;
And when the business of life is finished, is, after many a languid affection from the influence of—Sleep,
At last subjected to the general fate of all living bodies—Death.
These we imagine are the general properties of living bodies; and such is the order in which we are now to take a short and cursory view of them.
Sect. I. Respiration
Is that function by which air is brought into the system, and by which it is prepared in particular organs, that in some respect succeed the placenta in the general economy. For as any interruption of the usual intercourse between the placenta and fetus in respiration ovo proves soon fatal, so when that communication naturally ceases, and the new one succeeds between the lungs and external air, it is likewise found, that any supernatural interruption of this last is in all living bodies presently attended with various symptoms of increasing languor, and in many with an almost instantaneous death.
So essential is respiration to the system, that snails, chameleons, and some other animals, can live for years once to live upon air alone. We have seen a chameleon that lived ving bodies, and was vigorous for twenty-two months without any food, and which might have continued to live much longer but for an unfortunate bruise by a fall.
Other phenomena equally demonstrate the importance of air to the living body. The frog leaps away wanting its heart; it survives the loss of the greatest part of its spinal marrow. Without its head, it lives for some days, and its heart continues to circulate its blood (c). Spallanzani took one from the back of a female, cut off his head, and after performing this whimsical experiment, saw the gallant return to his mistress, grasp her in his arms, and finish the task which he had begun: And Borelli found, that cats and serpents, though their bodies be opened, and the whole of their viscera be taken out, are able to move for a day after; and yet notwithstanding, in all these animals, the life is observed to be suddenly extinguished when the all-vivifying air is excluded. Even the smallest insect has died, and the plant lost its vegetative power, when retained for any while in a vacuum. The fish itself, when placed under the exhausted receiver, has started anxiously to the surface of the water in quest of fresh air; and finding none, has sunk to the bottom and expired in convulsions.
(b) To give a general view of the manner in which living bodies are nourished and supported in the egg and uterus, and before they begin to depend entirely on their own organs, we have subjoined a plate (see Plate CCCXCI.), representing embryos of various kinds. The three first figures are from Swammerdam: the first is the membrane containing the insect, the second the membrane after the escape of the insect, the third is the insect itself, fed by absorbents, opening on different parts of the body.
The fourth, fifth, and sixth figures, are from Grew: the fourth is a bean, spreading its seminal roots into the lobes. In the fifth and sixth the lobes of the seed are seen converted into seminal leaves.
The seventh to the twelfth represent the transformations of the chick in ovo: the first of these figures is from Aquapendens; the rest are from Blasius, who got them from Malpighi.
The remaining figures are all from Aquapendens: the two last represent a fish that is sometimes oviparous and sometimes viviparous.
Plants and animals are here observed spreading their roots in a similar manner. The proper proportions are overlooked, not being necessary to convey the idea which is here intended.
(c) "Two days (says Dr Monro) after cutting off the head of a frog at its joining with the first vertebra, I found it fitting with its legs drawn up in their usual posture; and when its toes were hurt, it jumped with very considerable force. Its heart likewise continued to beat about forty times in a minute, and so strongly as to empty itself and circulate the blood.
"In several frogs, after cutting off the back part of the six undermost true vertebrae, I took out all that part of the spinal marrow with the cauda equina which they cover. The lower extremities were rendered insensible to common injuries, and lay motionless: yet the frogs lived several months thereafter, and the wounded parts of their backs cicatrised, and the bones of their legs which I fractured were reunited, the blood circulating freely in their vessels." Experiments on the Nervous System, made chiefly with the view of determining the nature and effects of animal electricity. If objections should be made to these trials performed in a vacuum, if it should be said that under the receiver the flinelled fruit swells and turns plump, that the body of the frog is strangely inflated, that its turpid eyes grow prominent in its head, and that thin phials corked full of air are broke by its expansion; still there are facts which do not admit of the like equivocal interpretation. All living bodies will die in the air which they have respired; and when ice covers the whole of the water, many of the fishes are known to perish; or if an opening be made in the ice, to halten to the air, and rather than retire, quietly suffer themselves to be caught.
To this general dependance of life upon respiration, there occur but few things like an exception; these are some serpents and worms and crustaceous animals found alive in the hearts of stones, some insects that were found in wood, and a number of toads which in different places have been taken from the hearts of trees and of rocks, where they left an impression, and where they were supposed in some cases to have lived for centuries without air. These facts, real or pretended, have been the cause of much speculation. Some philosophers, who imagine that nature is always obliged to act agreeably to those ideas which they have already formed of her laws, are notwithstanding the high authorities by which some of these facts are attested, disposed to doubt them. General analogy, which regularly opposes singular phenomena, is upon their side; and without her concurrence, they will grant existence to no living body that will not submit to the old established modes of respiration. Others again, who would not presume to dictate for nature, who have long experienced that she is not forward to obtrude her secrets, and who can believe that she may have still some to communicate, consider these facts as something new which she means to impart; and as one of the instances where she seems to deviate from general analogy in adhering to her grand accommodating principle by which she fits every living body for a certain range of varying circumstances.
These last, receiving the facts as sufficiently authenticated, have studied only how to account for them. When stones therefore were thought coeval with the world itself, they supposed their toads to have sprung from the ova that were scattered through the earth at its first formation; they did not recollect, that if the earth must have existed before these ova could have been sown, and that if the stones were coeval with the earth, the ova could not have entered their substance. When they afterwards learned that the consolidation of stones is an operation still carried on in the mineral kingdom, they acknowledged their ova to be less ancient, but did not perceive that all these ova involved suppositions that cannot be admitted, by sound reason. For how was an ovum to grow without air and without food? and how particularly was it to grow with such a force as to make an impression in a solid rock? This would imply a power of expansion scarcely to be equalled by gun-powder, and which we ought not to be rash in attributing to the nutritive effects of abstinence and nothing. Were it not for the toad, the expansion itself might have found a solution in a theory of the Earth, which has cast all its stones in a foundry under the water, where the moisture might have rendered them apt to be formed with numerous cavities.
Perhaps the way to remove these difficulties concerning the toad, would be to ascertain its mode of existence in the heart of the stone. Suspecting that the air communicated somehow with the solitary cell, we procured a toad that was crawling out from its den in the evening. It was put into a glass just large enough to hold it with ease. The mouth of the glass was filled with cork sufficiently close to retain water; the glass was then laid on its side, and the animal respired for several days without discovering signs of uneasiness: but supposing that air might still be admitted, the cork received a covering of wax, and the animal died ten hours after.
From this experiment, and the fate of toads when put under an exhausted receiver, from an air passage in the crust of chrysalids, from the porous texture of the white speck, or the opening which the snail leaves in the membrane that is spread over the mouth of its shell, we were led to think on d'Aubenton's remark, that the inclosed toads might have breathed, and that the wood has been always cleft, and the stone broken, before it was shown how the external air was excluded.
On farther reflection, our own experiment appeared inconclusive; and d'Aubenton's remark, after close examination, seemed not entitled to much attention. He p. 610, would have it supposed that a toad is lurking in every block of stone and of wood; and on this supposition would have an inquiry to be regularly made, whether or not there be any communication between this supposed animal and air; because, when the stone or wood is in fragments, the attempt to disprove such communication is in his opinion impossible.
But are we certain that the admission of external air would remove the difficulty? We are not so positive now as we were upon this subject. In the summer months, we recollect to have drowned frogs which were living in the fields, by keeping them some hours under water; but if we allowed them to rise to the surface, and respire at pleasure, they became at last so accustomed to that element, that if the temperature was not much above that of spring-water, they lay in the bottom not only for days but for weeks together.
In the winter season, it is well known that frogs are sometimes discovered in clutters below stones and under water in the neighbourhood of springs; and often seen in the bottom of ponds, marshes, and ditches, where water is collected, and the whole surface covered with ice. In this situation, we have frequently examined their sides and their nostrils, and can venture to assert, that they did not respire in the same manner that they did when on land: for the moment that this animal is put under water, the palpitating motions of its sides and its nostrils are observed to cease; and Chaptal has seen them suspending respiration as it were at pleasure even when in air.
While they move, however, and exhibit indications of active life, we would not say that air is excluded. In the roots of plants, in aquatic worms, in polypes, and in the placenta itself, the same organs seem to perform the double office of lungs and absorbents. When under water, what are the functions of these organs in frogs and in toads? It is not disputed that in moist places they can live longest without food; and some phenomena which have been observed relating to this subject appeared to us not unworthy of attention. In the beginning of the summer 1793, while we were making a few experiments on the nervous influence with some metals, a frog was taken out of the water in the dusk of the evening, and put into a deep and wide-mouthed glass till next morning; but next morning a quantity of water was found in the glass, the animal was dead, its mouth full of foam, and the greater part of its body covered with froth. The following autumn a boy came with a couple of toads wrapped up in tow. Till we had leisure to make our experiments, they were allowed to remain as they were for three days in the corner of a room. When taken out, their colour was pale, their bodies much swelled, and a quantity of water collected between the skin and the muscles. When held in the hand with their head upwards, the water was evacuated downwards by the anus. It was one of these toads that afterwards died when confined in the glass without air. Its body was put into a solution of madder for two days; and when the skin and muscles were removed, the bones, which are still preserved, were found red. A live frog in the same solution, though allowed to breathe, expired in a few hours. In three days its bones became of the red colour, but not so deep as that of the toad's. Another frog died in the solution; but the bones, from age or some other cause, did not receive the colour of the madder. In all cases the skins were found red.
As we know not how far the great accommodating principle of nature may be extended, perhaps the absorbents opening externally may in these animals sometimes supply the place of the lungs, as the lungs supplied the place of the gills which they used when tadpoles, and as the gills had formerly supplied the place of a placenta, or the primary absorbents, through which they derived their nourishment in ovo.
Those stones which inclose animals are known to be such as have gradually assumed the solid form, and those animals which have been inclosed are known to be such as in other cases have been subjected to the torpid state; But this state has not been examined with all the attention which it deserves. From this state, Bonnaterre says, in his introduction to Ereptology*, that it is impossible to rouse the animal by the loudest noise, the rudest shock, or the deepest wound; the internal motion is just sufficient to preserve the system from that decomposition to which animal substances are exposed. It retains only the form of what it was. It appears neither to live nor to grow; and the whole mass, if what is exposed to the air be excepted, is not sensibly altered while the torpor continues. All the senses are shut up; all their functions are entirely suspended: digestion is no longer in the stomach; all respiration has apparently ceased; and it has been doubted whether or not this function be in some cases at all retained. When the genial warmth, however, returns, in six, in eight, or in ten months, according to that variety of climates between the frigid poles and the tropics, the animal revives. But the question is, if the first circumstances in which the animal became torpid had been artificially or naturally continued, how long in this way might the different functions of life have been suspended; and how far are we warranted by the analogy of seeds and of eggs to lengthen this period of their existence, without supposing a decomposition or destruction of organs?
Experiments must tell what are the limits which nature has here prescribed to herself. New eggs, when covered with varnish, or placed under the exhausted receiver, are secured against the attacks of corruption. Bomare, in his Dictionary, has mentioned three, which, protected from air, were found fresh in the wall of a church after a period of 300 years (d).—And if it be true that a snake found in a block of marble died as soon as exposed to the air, or if the parts in contact with air be the only ones which in torpid animals appear to be changed, it would seem probable that a total exclusion of this varying and active element would tend more to the preservation of torpid animals, in certain instances, than a free admission, which, in those cases where all vital functions have ceased, is regularly found a principal agent in their dissolution.
M. Herissant of the French Academy was the first Herissant's philosopher who, by means of experiment, thought of experimenting nature herself upon this subject. On the 21st of February 1771, he with great accuracy shut up three toads from the air, two of which were taken out alive on the 8th of April 1774. D'Aubenton says† that after a period of 18 months; but in this instance we depend more on the friend‡ of Fontana, who has mentioned the dates. The two toads were again inclosed, and Herissant died before there was a second inspection. D'Aubenton says, that when taken out their bodies were hard and shrivelled, and their whole mass, if what is exposed to the air be excepted, is not sensibly altered while the torpor continues. All the senses are shut up; all their functions are entirely suspended: digestion is no longer in the stomach; all respiration has apparently ceased; and it has been doubted whether or not this function be in some cases at all retained. When the genial warmth, however, returns, in six, in eight, or in ten months, according to that variety of climates between the frigid poles and the tropics, the animal revives. But the question is, if the first circumstances in which the animal became torpid had been artificially or naturally continued, how long in this way might the different functions of life have been suspended; and how far are we warranted by the analogy of seeds and of eggs to lengthen this period of their existence, without supposing a decomposition or destruction of organs?
(d) See Bomare, under the article Œuf; and a fuller account of the same eggs in the Dictionnaire de Merveilles de la Nature, under Œuf. absorb the animal fluids, like the plaster used by the French academicians.
One of the toads was heard to croak after being inclosed. In making their experiments, has it, therefore, been thought a matter of indifference by the French philosophers, whether the animal was immersed alive in the full exercise of all its functions, or existing only in its torpid state? and with respect to this singular state, (might not the questions be fairly put), have its several kinds, have the causes which induce it, or those degrees to which it may be carried in different animals, been yet ascertained? Is not our knowledge of the torpid state at this moment principally the result of casual observation? Has it not been oftener than once supposed that the torpor of all animals is similar, or takes place to a similar degree? Have not torpid animals been therefore spoken of in general terms? and has it not been asserted that they retain a portion of heat and internal motion? though some have been found congealed in the ice, and many been dried to such a degree that they could be revived only by moisture.
"That snakes and fishes, after being frozen, have still retained so much of life as when thawed to resume their vital functions, is a fact," says Mr Hunter, "so well attested, that we are bound to believe it." How came it, we would ask, that fishes which had been frozen by this truly ingenious physiologist never recovered? He recovered parts of different animals which had been frozen? Had the snakes and fishes of which he had heard been only partially congealed in the ice? or had the fishes which he selected for these experiments been properly chosen? or may all animals with equal fairness be made the subject of such experiments? and may all transitions from heat to cold, and from cold to heat, whether slow or rapid, if not in the extremes, be viewed as nearly of the same consequence? Are all feasts and conditions of body equally favourable to this state of torpor? and will these causes which induce torpor by operating externally in the months of autumn be able to continue it by the like action in the months of spring? We can answer, no.
It has been said that animals subsist in their torpid state by the reabsorption of fat. Has it therefore been proved that all animals, not to say living bodies, are possessed of fat? or if they be, has it been demonstrated that they have a superfluous quantity to be reabsorbed? Has it been shown that their waste of fat is always occasioned by this reabsorption; or has this reabsorption in all cases been of that kind to counteract the effects of abstinence? If it has not been proved that all animals contain fat, and that this fat is reabsorbed in their torpid state, ought not the general assertion to be limited? Granting that in many respects it were true, have not philosophers been here amusing themselves with logic, where they could have been employed in making experiments? Have they not ventured to give us conclusions, where we had reason to expect facts? and on this account has not their conduct been somewhat similar to that of navigators who, sailing along the coast of Patagonia on one side, and observing a few men of an uncommon stature, have from thence peopled the whole of the country with a race of giants? or rather to that of some calculators, who, from seeing a few parts of a continent, have ventured to give a map of the whole, to describe kingdoms that are yet unexplored; and by their skill in addition and subtraction to exhibit the figure, the extent, and proportion of lands unknown?
Leaving therefore the torpid state as one of those subjects with which we at present are little acquainted, and of which we therefore cannot speak with certainty in the general abstract language of science; it will naturally be asked, In what respect is air so necessary to all living bodies in their active state, and how it contributes to the regular performance of the different functions?
The ancients, who were led by the heat of the blood to suppose a vital spark in the heart, who had noticed the appearance of smoke in the breath, and who had observed that fire was extinguished when deprived of air, naturally inferred that the end of respiration was to support their imaginary flame, to ventilate the blood in the arteries and lungs, and to keep alive their vivifying spark. They were far, however, from being agreed as to the manner how this was effected. Some were of opinion that a certain principle of the air was absorbed, to which they gave the name of the producer of life, or the food of the spirit; while others were persuaded that the air acted as a refrigeratory, and was merely intended to moderate the fire, to assist in expelling the fuliginous vapour, and preserve the system in an equal temperature.
The moderns, who, after all their researches, have been unable to discover this vital spark of the ancients, are more puzzled to assign an adequate cause for the heat than for any cold which they discover. To account for this singular phenomenon, they have been ransacking nature for causes; and perceiving that putrefaction, mixture, and friction, are in many instances accompanied with heat, have thence conjectured that they sometimes operate in producing the warmth of the living body. But there are theories which have been imported from the hot-bed, the laboratory, and mechanic's shop, and which have never yet been countenanced by physiological facts and observations. No one has been able to show that putrefaction exists in a healthy state, except in the feces: no one has proved that any mixture which regularly occurs in the elementary canal or vessels, generates heat; and though friction has been a favourite hypothesis, yet those circumstances, in which it evidently produces heat, have not been discovered in the living body; and it is not determined whether it be there a friction of the fluids, a friction of the solids, or a friction of the fluids and solids together.
Of animal heat, the most rational theory, we think, is one which properly belongs to the last century; it Verheyen, is confirmed by modern discoveries, and has ascribed this heat to respiration. Many had observed, that those animals which respire most have the warmest blood (e).
(e) Quod autem animalia calidiora fortius respirent, non probat respirationem illis potius datam esse, ad sanguinis refrigerium, quam calorem illum intenfum produci a validiori respiratione: imo posterius non tantum æque, at magis probabilis appareat: quia secundum omnium tentationem calido vivimus, frigido extinguimur. Lower demonstrated, that this blood received a new and a brighter colour in passing through the lungs (r). Verheyen and Borelli both proved, that the air lost something by coming in contact with that organ (c). Mayow showed, that this something which the air loses is contained in nitre (h). Experience taught the workers in nitre, that this something was absorbed from the air (i): and Verheyen remarked, that it is also absorbed by the lungs; and is probably that which maintains combustion; which qualifies the air for giving support to animal life, and imparts to the blood the vermilion colour (x).
How well the whole of this reasoning was founded, is proved by the late discoveries of Priefley and other chemists. There is now obtained, in a separate state, an aerial fluid, which maintains both life and combustion, and gives a vermilion colour to the blood. It is extracted in a very large quantity from nitre; is one of the component parts of the atmosphere, and the vital principle of that element; without which, in most animals, life is extinguished. From some phenomena which happen in combustion, it has been termed principium fortis. It was called deplogisticated air by Priefley the first discoverer; as the great acidifying cause in nature, the French nomenclature has given it the name of oxygenous gas; and, as one of the causes on which the existence both of fire and of life depends, it is named empirical or vital air.
Late discoveries have shown farther, how this air may in respiration produce heat. From the most accurate investigations, it appears, that caloric, or the principle of heat, is a distinct substance in nature; that it combines with different bodies in different degrees; that it is the cause of fluidity in all; and that, in proportion to that capacity which they have for it, and to that distance at which they are removed from the fluid state, the more or less caloric they contain. Aeriform bodies being all therefore exceedingly fluid, it must be evident, that when they are fixed or condensed in the blood, and made to approach nearer solidity, a quantity of heat must be evolved. A part of this is very plainly evolved in the lungs where the air is absorbed, as appears by the breath; and a part evolved by the action of vessels, as appears from nearly an equal heat over the system, from the partial heat of a morbid part, and the sudden transition from heat to cold, and from cold to heat, over the surface, when the vessels are affected by either internal or external stimuli. When the heat, thus evolved by the gradual fixation of that body with which it was combined, has been successful in making its escape by the lungs and integuments, the blood returns in a dark and sluggish stream by the veins, and mingles again with the genial fluid, which before gave it spring, activity, and life.
Of that oxygen which remains in the system, part is employed in forming different saline combinations and supplying the waste occasioned by that constant resorption; which, from many experiments that have been made with solutions of matter, is known to take place in the solid bones. The use of that oxygenous gas which returns with the breath, is best understood after knowing its affinities. Its basis oxygen, combining with hydrogen, which is the basis of inflammable air, forms water; and combining with carbone, the carbonic acid. It carries, therefore, back with the breath a part of the carbone produced by the slight combustion of the blood, and a quantity of hydrogen arising from the watery fluid decomposed.
But oxygenous gas does not alone enter the lungs. Of gases which 100 parts of the atmosphere, but 28 are oxygenous gas, containing 76% of carbonic acid, and 72 are azotic gas (L). These last, which we though intended chiefly for other beings different from man, which are in immense numbers on the globe, but their which, like him and the nobler animals are not formed in respiration.
Ut proinde non videatur aliquid a natura datum esse, quo intenditur frigus vitae contrarium. Verheyen, Tract. 2. cap. 7. de Uso Respirationis.
(r) Postquam circulatio sanguinis innuit, diu creditum fuit sanguinem venosum colore illo coccineo rufus indui in ventriculis cordis, et praecipue ubi calor, quem judicabant illius coloris authorem, est intuentior: At negotium istud peragi in pulmonibus, nempe respirationis beneficio, evidenter offendit cl. Lowerus experimentis. Ibid.
(c) Inquiramus quale sit istud aereum adeo nobis et multis animalibus necessarium. Ut ejus defectu vita extinguiatur citissime. Vulgaris enim aer dici non potest, cum illum per meatus notabiliores sanguini immittit conveniret, fitque experientia certissimum, animalia respirantia non tantum aëre simpliciter; sed etiam recenti continuo indigere, unde concludendum est tantummodo aliquas particulas subtilliores ab aëre fecerni, et maës sanguinis immiscenti, quibus spoliatus ad ulteriorem respirationem sit indoneus.
(h) Et quidem verisimile est, inquit Mayow, particulas quasdam indolis nitrofalsae, easque valde subtiles, agiles, fummeque fermentatives ab aëre pulmonum ministerio fecerni, inque cruris maës transmitti. Adeo enim ad vitam quamcumque fal, istuc aëreum necessarium est, ut ne plantæ quidem, in terra, ad quam aëris accessus precluditur vegetari possint; fin autem terra ista aëri expofita, fale hoc fecundante denuo impregnetur, ea demum plantis alendis iterum idonea evadet.
(i) In aëre autem quid nitrofum contineri norunt ipsi vulgaris nitri confectiones, qui terram aut laterum fragmenta ex quibus nitrum elixiri intendent, aëri liberiori diu multumque exponunt; utque ab eodem undique ea tangente ac persuffiente uberioris impregnetur, sæpius vertunt, atque ita fuorum sumptuum et laborum ampliorem mellem mercedemque referunt.
(k) Infupere, si post confectionem nitri terra aut laterum fragmenta exponantur libero aëri, ea demum post aliquod temporis spatium, quodam fale nitrofo abundabunt. Est autem verisimile, aerem gratia ejusdem materiae et vitae nostræ continuationi et ignis accensioni necessarium esse; praecipue ovm rufus experientia docet ruborem sanguinis e corpore educiti, per additionem falsis nitri intensum iri in eodem profus modo secuti, per respirationem in corpore vivente. Ibid.
(l) These are nearly the proportions. ed to breathe the empyrean air, must notwithstanding be of some important and essential use to all living bodies. It has accordingly been found by experiment, that pure and unmixed oxygen gas cannot be breathed for any very considerable time without danger; that some azote is contained in the blood, and has been extracted from the muscular fibre, when properly treated with the nitric acid. According to Berthollet, five of its parts with one of hydrogen forms ammonia or volatile alkali; which dispels the glandular tumours of the body, and prevents the coagulation of blood and the thickening of mucus which arise from acids (m). The azotic gas may therefore in part unite with hydrogen, may prevent the coagulation of serum, the catarrhous formation of viscid mucus, and many combinations that oxygen might form, injurious to the system. The carbonic acid, which is $\frac{1}{2}$ of carbure and $\frac{3}{4}$ of oxygen, may also be necessary in regulating the effects of the other two. In aerated water, its uses are very generally known: it allays the pain of the urinary bladder when excited by calculus; it has been employed in the cure of wounds, and been thought useful in the pulmonary phthisis. It is generated in the lungs of those animals which respire oxygen. In small proportions it favours the growth of the vegetable tribes. These tribes readily decompose it; and, with the addition of other prepared oxygen from water, restore what is pure to the general mass of the vital fluid, that plants and animals might thus live by the mutual performance of kind offices.
We return again to animal heat. Every theory that pretends to account for animal heat, ought also to account for that singular equality of heat which the system preserves, or endeavours to preserve, in different temperatures. The above theory explains it simply in the following manner.
Venous blood, if exposed to the air, is known to absorb a portion of oxygen, and assume that colour which it has in the pulmonary veins and aorta. Suppose an absorption of a similar kind taking place in the lungs, a fact which may be proved by decisive experiments; it is plain that the oxygen by this absorption must recede from its gaseous or fluid state; that a quantity of heat must be therefore evolved, which, along with the heat of the refulgent blood, is carried away by that vapour which issues from the lungs. In the course of circulation, the oxygen will naturally incline with hydrogen to form water; it will tend likewise to the formation of many other compounds; and, as it enters into new states, and is farther removed from gaseous fluidity, it must still be giving out a portion of heat. If the surrounding temperature be cold, this separation will be easily effected. The caloric will, in that case, be greedily absorbed from the interior surface of the lungs and exterior surface of the whole body. The oxygen, meeting with the necessary temperature, will readily pass into new forms; and the venous blood returning to the lungs, will demand a supply which will be either greater or less according as the cold, by favouring the escape of the caloric, and promoting new combinations with oxygen, had removed it from the point of usual saturation.
The gradual evolution of heat is a proof that the temperature must be sometimes reduced before the oxygen can properly enter into all the usual combinations of the system. Suppose the body then to be placed within a hot circumambient atmosphere. This atmosphere, if warmer than the animal, will be more apt to part with heat than to receive it; and the oxygen absorbed, being thus unable to dispose of its caloric, will be prevented from passing into those combinations and forms where heat is evolved. The venous blood will therefore conduct it back to the lungs, and make a demand for a new supply; but proportionally less according as the hot circumambient air, by preventing the escape of the caloric, and the usual facility of new combinations, has confined its removal to a smaller distance from the point of saturation.
In this last case the thing principally entitled to notice is a very curious effort of nature to resist the growing increase of heat. In the warm atmosphere, as during violent muscular exertion, the exhaling vapours is commonly discharged in a greater quantity from the surface of the body; and consequently the heat furnished with an excellent temporary conductor, that in some measure counteracts the dangerous effects from without.
After all, the reader is not to suppose that he here has received a general theory of respiration. All living bodies are not supported by the same kind of aerial food. Oxygenous gas has indeed been honoured with the flattering appellation of vital air; and nitrogenous gas been usually distinguished by that degrading epithet azotic; a word which signifies destructive of life. But though man, and all the warm-blooded animals that have yet been examined, may die in respiring the nitrogenous gas, this gas however, which constitutes more than two thirds of the whole atmosphere, may in general be called the vital air of the vegetable tribes, and of not a few of the orders of insects which thrive and live in it. For while man, and others which respire as he does, emit both the hydrogen and carbure, and return the nitrogen not sensibly diminished; most vegetables and many insects eagerly inhale them, and emit oxygen as noxious or useless. These effects are the indications of a radical difference in constitution. Even the fibres of those living bodies which exhale oxygen, will, after death, attract it so powerfully, as to decompose the nitric acid; but those bodies which inhale nitrogen, have so very weak an affinity to oxygen, and so strong a one to some of the bodies with which it is combined, that they can easily decompose water and carbonated air.
What fishes respire is not ascertained. Neither the change of the air, nor of the water which they occasion when in close vessels, have, so far as we know, been fully examined. Chaptal is assured, that, like other animals, they are sensible of the action of all gases. Fourcroy has ascribed to a too great absorption of oxygen.
(m) Weak volatile alkali dissolves mucus, whose morbid viscosity Fourcroy has ascribed to a too great absorption of oxygen. croy says, that they do not generate the carbonic acid; and that the air which Priestley and he found in the air vessels of carp was nitrogen gas. Their thermometrical heat is so low, that in D'Aubenton's table they are reckoned among the cold-blooded animals.
The temperature of plants is still lower. The heat of a tree which the very ingenious Hunter examined, though several degrees above that of the atmosphere when below the 5th division of Fahrenheit, was always several degrees below it when the weather was warm. When taken out, the sap was observed to freeze at 32°; while in the tree, it would not freeze below 47°. The very profuse perspiration of vegetables greatly moderates the heat in their surface; and as air which absorbs moisture expands, and becomes thereby specifically lighter, there is a regular current produced, and evaporation rapidly promoted by the dense air displacing the rarefied.
To adopt here a general language with respect to the heat which is developed in all living bodies, it is proportioned to the quantity of matter which is by means of the vital powers reduced to a state more nearly approaching solidity; to the kinds of substances which are reduced, and to the degrees and kinds of the reduction.
In all living bodies there appear to be certain degrees of heat, peculiarly fitted for carrying on their various economical operations. What these are, in the different kinds of plants and animals, is not known.
The bear, the hedgehog, the dormouse, and the bat, may probably not digest when reduced to 70°, 75°, or 80°. The frog, however, will digest at 60° (N); and greefs of the birch before it arrives at 47° (O). It would seem that respiration, besides imparting aerial food, was intended to preserve and regulate these different degrees of heat. It raises the heat after a meal; it fusters it to fall in the time of sleep; it withdraws the supply when the atmosphere is warm, and increases it again when the atmosphere is cold. It should therefore be remembered, that heat merely is not the object which is solely aimed at in respiration. All living bodies have their congenial degrees of heat. The regulation of these is important: on the one side, it prevents the by respiration, diffusion, on the other the coagulation, of their fluids; it preserves the living power of their organs; and, by a natural and proper temperature, affords their action in mixing, composing, in decomposing, and in variously preparing the different parts for secretion, excretion, absorption, reabsorption, and assimilation (P).
As various fixations of the vascular fluid are regularly taking place in the different parts of the living body, and as air is not the only fluid concerned, it should almost be unnecessary again to observe, that the whole of the heat is not evolved in the lungs, nor the whole that is evolved disengaged from air.
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(n) See observations on certain parts of the animal economy by Mr Hunter. We allude here to his experiments and observations on animals, with respect to the power of producing heat.
(o) See Dr Walker's excellent Paper on the motion of the sap in trees, 1st volume Philosophical Transactions, Edinburgh.
(p) The ingenious Dr Crawford has published a theory of animal heat different from that which we have here presented to our readers. Assuming as a fact, that heat and phlogiston are two opposite principles in nature, he goes on as follows:
"Animal heat seems to depend upon a process similar to a chemical elective attraction. The air is received into the lungs containing a great quantity of absolute heat; the blood is returned from the extremities highly impregnated with phlogiston; the attraction of the air to that of the phlogiston is greater than that of the blood. This principle will therefore leave the blood to combine with the air: by the addition of the phlogiston, the air is obliged to deposit a part of its absolute heat; and, as the capacity of the blood is at the same moment increased by the separation of the phlogiston, it will instantly unite with that portion of heat which had been detached from the air.
"We learn from Dr Priestley's experiments with respect to respiration, that arterial blood has a strong attraction to phlogiston (become a vague word with different meanings in different authors). It will consequently, during the circulation, imbibe this principle from those parts which retain it with the least force, or from the putrefactive parts of the system; and hence the venous blood, when it returns to the lungs, is found to be highly impregnated with phlogiston. By this impregnation its capacity for containing heat is diminished. In proportion, therefore, as the blood which had been dephlogisticated by the process of respiration becomes again combined with phlogiston in the course of circulation, it will gradually give out that heat which it had received in the lungs, and diffuse it over the whole system.
"To account for the stability of animal heat, he observes, that as animals are continually absorbing heat from the air, if there were not a quantity of heat carried off equal to that which is absorbed, there would be an accumulation of it in the animal body. The evaporation from the surface, and the cooling power of the air, are the great causes which prevent this accumulation: and these are alternately increased and diminished in such a manner as to produce an equal effect. When the cooling power of the air is diminished by the summer heats, the evaporation from the surface is increased: and when, on the contrary, the cooling power of the air is increased by the winter colds, the evaporation from the surface is proportionally diminished." See Crawford on Animal Heat, p. 73—84.
Besides, supposing that the principles of fire and inflammability are opposites in nature; this theory supposes that the blood, while in the lungs, gives out phlogiston and takes in heat; but that, during the remaining course of circulation, it gives out heat and takes in phlogiston: it supposes, that this phlogiston is collected from parts that retain it with little force, or from the putrefactive parts of the system; it is not said where: it It may farther be remarked, that the whole of the air does not enter by the lungs; much is contained in the liquid and solid parts of the food. It is extricated often in the process of digestion; and when the organs are vigorous and healthy, is made subservient to the general economy. If the organs, however, should happen to be languid, it seems their authority, which cannot be enforced; from being friendly, it soon becomes inimical to the system, and threatening danger accumulates, not only in the stomach and intestines, but in other cavities. It has been found in the cellular membrane; in certain vessels formed for itself; in the uterus; in an abscess; and in gun-shot wounds: It has sometimes burst from the vagina with a sort of noise*. And in a nephritic complaint of a horse, we have observed it flowing in a stream from what the farriers denominate the fleath.
In some kinds of aquatic plants, in eggs, and in a variety of fishes, there are certain vessels containing air, which seem to have certain necessary functions allotted them by nature. In the plants and in fishes they were once supposed to have been wholly intended for swimming (Q). It was remarked, that those fishes which remain constantly at the bottom of the water have no air vessel; and that a fish whose vessel was burst by means of the torricellian vacuum, though it lived for a whole month after in a pond, was never able to rise to the surface+. The practice, however, which some fishes have of ascending at times to inhale air, and descending after their vessel is filled‡; the communication which, in some fishes, this air vessel has with the stomach; that power in the pigeon and some other birds of introducing air into the crop ||; and lastly, the air which is uniformly found in impregnated eggs—would tempt us to believe that these natural collections of air, with their other uses, may perform some essential service in nutrition.
Having explained the general intention of respiration, we are now to inquire, what are the kinds of respiratory organs, and in what manner their functions are performed? The preceding table has in some measure made us acquainted with this subject. Some animals breathe by a trachea and lungs; insects, by either stigmata or tracheæ, opening into air vessels; plants, by air vessels and leaves; fishes, and numbers of the watery element, if they do not breathe, at least receive air by their gills; the fetus in ovo, the polypus tribe, and many more organized bodies, by the same organs which convey their food.
The absorbents appear to be the first and most general way by which living bodies are supplied with air: the mouths of these vessels are like small tubercles, scattered over the body of the insect while wrapt in its membrane. In the horse and the bird they are blood-vessels spreading on a membrane, and deriving nourishment from the uterus or egg, that had been itself nourished by absorbents: In a cow, they are vessels which, foreading on a membrane, terminate in glands; these glands being opposite to others which adhere to the uterus; and the membranous and uterine glands, when in contact, inclosing a third gland like a kernel. In man, they are vessels spreading on a membrane, and entering a large glandular body called the placenta. In the mouse and the hare, they are likewise vessels branching on a membrane, and entering a placenta: this placenta, when it happens to be fixed, receives large veins from the parent, and which may be either inflated or injected from the cavity of the uterus.
Those which are properly respiratory organs, exercise not their function till circulation and nutrition are in exercise begun: though, if the observation of Garman be just, for their that the air may become a real food for the class of functions, spiders, or if it be true that the larvae of ants as well as of several insects of prey, increase in bulk, and undergo their metamorphoses without any other nourishment than air §, this law is not universal. It may, however, be doubted, whether some moisture be not absorbed. With regard to the ant, we have reason to suspect that the observations on which such a conclusion was founded have not been accurate.
Not only are the respiratory organs thus late in exercising their functions; in many vegetables a great renewal, part of them is annually renewed and laid aside in the sometimes torpid state. In those insects which undergo the most remarkable kinds of transformation they suffer a change; and in all those animals which spend their earlier days in the water, and afterwards come to live in the air, they are altered in kind.
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*See Observations on Digestion, by the late Mr Hunter.
†Borelli de Motu Animalium, cap. 23.
‡De Natatu, prop. 89.
||Chaptal's Elements of Chemistry, vol. i. § 5.
||Anatomical Description of the Domicelle of Nymphida, by the French Academy.
§Chaptal's Elements of Chemistry, vol. iii. § 1.
Art 5.
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Supposes that the blood, in passing through the lungs, receives heat only: that the whole of this heat is evolved in the lungs by precipitation; and is thence diffused over the system as from a centre or focus; in which case, we must also suppose that the lungs are the warmest part of the body; and that the heat of the other parts will be in proportion to their distance from the lungs, or the length of the vessels through which it has passed.
As for the stability of animal heat, this theory ascribes it entirely to foreign causes; to the different degrees of evaporation; or to the varying states of the air.
The singular meaning which this theory gives to the word phlogiston, must strike every one who knows the etymology of that word. The celebrated Stahl found it in the Greek; and applied it naturally to signify pure elementary fire, or the most pure and simple inflammable principle in a state of combination. Mr Kirwan has since used it to express hydrogen: Dr Priestley has called the azotic phlogisticated air: and Dr Crawford, who seems to take phlogiston in the sense of Mr Kirwan, speaks likewise as if he understood it in the sense of Dr Priestley. Mr Kirwan's phlogisticated air, however, will not kindle without oxygen: Dr Priestley's will extinguish fire: and Dr Crawford's is directly opposed to that principle. These are not the ancient doctrines of Stahl; they are new ideas expressed in one of his antiquated words; the meaning of that great man is neglected. The sounds which he uttered, like the dead language of an old ritual, are among a few still in veneration.
(Q) Borelli has shewn how, by contracting the air vessel or allowing it to expand, the fish can rise, sink, or remain stationary in the water. Borelli de Natatu. In all living bodies the proper function of one part of the respiratory organs is, to secrete from the water or air that particular aeriform fluid which mingles with their juices, and which is necessary to life and nutrition. In many cases these organs are placed externally, and are always in contact with the air or water from which they secrete. In other cases they are lodged internally; and air or water are then alternately admitted and expelled by varieties of organs which serve as auxiliaries.
The plants secrete their aeriform fluid from water and air. They receive air along with the liquids of their absorbents, which open on the roots, the trunk, and the branches, and upon the inferior surfaces of leaves; or, if nature has plunged these leaves under water, the absorbents open and imbibe their fluids on both sides. In many, however, the upper surface of the leaf is intended to inhale air. Bonnet observed, that when this surface was applied to the water the leaf died soon; but that when the lower surface was applied, it lived for months. It has also been remarked, that the upper surfaces of some leaves will repel water; and that the death of the leaf will ensue when its breathing pores are obstructed with oil*. We hence learn why aquatic plants rise up to the surface of the water and spread their leaves in the open air; and as it is proved by Ingenhouze and others, that the respiration of many leaves is assisted by light, we see a reason why plants growing in a dark room turn to the place where light is admitted; why the flowers and the leaves of many plants follow the diurnal course of the sun; why the branches of trees, which require much light, die when placed in a thick shade; why moonshine in autumn contributes so much to the ripening of grain; and why leaves and branches are arranged in such a manner as least to intercept that quantity of light which nature has allotted to the genius of each.
The air vessels in the body of plants are those vessels which contain juices but at certain times, and which during the greatest part of the season are filled with air†. This air is collected from the sap of the roots as it passes along the diametral infusions, and from those vessels which open upon the trunk and upon the leaves‡. Like pulmonary tubes, which are seen branching through the bodies of insects, they perform an office similar to that of the tracheae and bronchia; and are those general receptacles of air from which the neighbouring parts of the plant secrete what is needed: for in plants and a certain number of insects, the functions of the lungs, the stomach, and the heart, are generally diffused. The several parts can respire, digest, and circulate fluids on their own account; and if they should chance to be severed from the whole, can live and grow, and propagate their kind.
The air vessels are surrounded by those which contain a liquid during the whole time of the growth. They are the largest vessels of the wood, as distinguished from the bark; and in the leaves they may sometimes be seen even without the assistance of glasses. Their cavity is formed by certain fibres which wind spirally like a cork-screw. In the leaf they generally approach and recede like the filaments of nerves; but they never inoculate from one end of the plant to the other, except at the extremities §; they resemble the pulmonary tubes of insects by their general dispersion over the system, and the spiral rings of which they are composed (a); they differ in this, that the pulmonary tubes are frequently observed to anastomose in their larger branches, as the ramifications of a vein or arteriovenous twig do in their smaller capillary twigs.
The respiratory organs, which are similar either to the gills of fishes or the lungs of man, can hardly here claim a description, as their nature and forms are so generally known. There is one circumstance, however, in birds which arrests our attention: the cells of their bones, and the numerous vessels of their soft parts which communicate with the lungs, have been deservedly a matter of surprise to most physiologists. In accounting for their use, the ingenious Hunter and supposes that they lessened the specific gravity and ions contributed by them being the circumstance which he termed the thought most peculiar to birds. Learning afterwards that they were in the ostrich and not in the bat, he in birds, supposed that they were appendages to the lungs. In &c., amphibious animals, in the snake, viper, and many others, he observed, that "the lungs are continued down through the whole belly in form of two bags, of which the upper part only can perform the office of respiration with any degree of effect, the lower having comparatively but few air vessels (s)." In these animals, the use of such a conformation of the lungs was to him evident. "It is in consequence of this structure," said he, "that they require to breathe less frequently than others." From this reasoning he naturally
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(a) See the spiral rings in the pulmonary tubes of a bee, Plate XVII. fig. 10. Swammerdam's Book of Nature, or History of Insects.
(b) The same observations were long ago made by the immortal Harvey. After observing that both the transverse and longitudinal membranous diaphragms of birds contributed to respiration, he adds, "Et alia, ut nunc taceam. Aves praeceteris animalibus non modo facillime respirant, sed vocem etiam in cantu diversimode modulatur: cum tamen ejus pulmones lateribus et costis adeo affixi sunt, ut parum admodum dilatari, afflurgere, et contrahi possint.
Quinteniam (quod tamen a nemine hactenus observatum memini) earum bronchia five asperae arteriae fines in abdomen perforantur. Aëreoque inspiratum intra cavitates illarum membranarum recondunt. Quemadmodum pisces et serpentes intra amplas vesicas in abdomine positas, eundem attrahunt et reservant, eoque facilitius natare exiftimantur. Et ut ranae ac bupones cum æstare vehementius respirant, aëris plus solito in vesiculas numerosissimas absorbent (unde earum tam ingens tumor) quo eundem postea in coactione liberaliter expirant. Ista in pennatis pulmones potius transitus et via ad respirationem videntur quam hujus adequatum organum.
De Generat. Animal. Exercit. 3. turally inferred, that the motion of flying might render the frequency of respiration inconvenient; and that a reservoir for air might therefore become singularly useless. The bat and the ostrich, however, are here as formidable objections as before. The bird respites frequently when at rest, and when it flies to our bosom from the hawk; that frequency seems to have been increased by what is a general and common cause, an increased degree of muscular exertion. Had air cells been intended merely to prevent the effects of a rapid motion on respiration, we might expect to see them in greyhounds and a number of quadrupeds, much more readily than in some birds whose flights are neither rapid nor long.
This great physiologist was not aware that the circumstance most peculiar to birds was not their act of flying, but their feathers, which contain a large quantity of air, and which require a regular supply, whether they soar on the wings of the eagle, or remain on the ground, attending the ostrich (t).
Both in amphibious animals and birds, the air of the vesicles has passed the respiratory surface of the lungs. In the trachea of plants and the pulmonary tubes and vesicles of insects, it is only proceeding on its way to be respired. Would it be worth while to inquire whether vegetable substances, and those which are called corneous in animals, require a different preparation of air from what is the common preparation of lungs? whether hair grows best, or the cuticle thickest over soft parts that are cellular and spongy (v)? and whether the animals that bear horns have larger sinuses in the frontal bone of their cranium than others? From the general diffusion of air through the birds, and the situation of their vesicles beyond the lungs, it would appear that the pulmonary viscera in these animals does not respire or secrete air for the whole system; and we are certain, that in plants and insects most parts respire the air for themselves, and that there is no particular part appointed to secrete air for the whole.
We here speak of respiratory organs as those which Air absorbs, secrete an aeriform fluid from water and air; but our eddy the language probably had been more accurate had we called them the organs in which an aeriform fluid is absorbed by their liquid contents, as these flow by, tory fur either wholly or in part, in their course through the face system. It was long denied that any absorption of the air took place from the pulmonary surface; and speculative reasoners had attempted to prove that no air could pass to the blood through the membranes of the lungs, because air had refused upon some occasions to pass through pieces of wet leather that had been exposed to it for that purpose. Borelli, however, endeavoured to show how air in the lungs might mingle with the blood, and how some ways disappeared in respiration. There are few doubts now entertained on this subject. Venous blood inclosed in a bladder by the celebrated Priestley discovered such an attraction for oxygen, that it absorbed the aeriform fluid through all the coats of the resisting medium, exhibiting an instance and beautiful illustration of the chemical affinities which take place in this function.
The reader will observe, that the two words respi- Two kind ratory organs are here employed in what may be ra- of respiration ther a particular sense. The truth is, there are two kinds of respiratory organs, which, though sometimes included in the general expression, should always be considered as perfectly distinct. The first kind comprehends those in which the water and air is decomposed; the second, those by which these fluids are properly applied to the respiring surfaces of the former. We observe these last in the fluttering motion of the leaf itself, or in that tendril which turns the surface of the
(t) "The use of this retention (of the air in the vesicles of birds) is not well known to us, at least in respect of the upper pouches; so in regard of the lower ones. The use of this retention has been explained in the description of the ostrich: where it was shown that there is a probability that the air contained in the lower pouches serves to compress the visceras, and make them rise upwards. Some do think that this retention of air serves birds to render them lighter in flying, like as the bladder which is in fish helps them to swim. And this conjecture would have some foundation, if the air contained in the bladders of birds were as light in proportion to the air in which they fly, as the air contained in the bladders of fish is in proportion to the water in which they do swim. But to say something which hath at least a little more probability, waiting till we have a more certain knowledge of the truth and use of this retention of air, we consider that the birds generally rising very high, and even to the place where the air is a great deal lighter than it is near the earth, might be deprived of the principal advantages of respiration for want of an air whose weight might make on the heart and arteries the compression necessary to the distribution and circulation of the blood. If they had not the faculty of containing a long time a portion of air, which being rarefied by the heat which this retention produceth therein, might, by enlarging itself, supply the defect of the weight of which the air that they do breathe in the middle region is destitute. For if there be a great many birds which do never rise very high into the air, whose lungs have notwithstanding these bladders in which the air is retained; there are also a great many that have wings which they use not for flying. And it may be observed, that there are found some parts in animals which have not any use in certain species, and which are given to the whole genus, by reason that they have an important use in some of the species. It is thus that in several kinds of animals the males have teats like the females; that moles have eyes; ostriches and cassowaries wings; and that land tortoises have a particular formation of the vessels of the heart which agrees only with water tortoises, as it is explained in the description of the Tortoise." The Anatomical Description of a Cassowary, by the Royal Academy of Sciences at Paris. We can hardly answer for the justness of this reasoning, which maintains that the genus has useless parts merely in complaisance to the species.
(v) Nails and hair grow after death, and a quantity of air is evolved in putrefaction. the leaf to the sun. We see them producing these oscillatory motions in the branching gills of the puix arborescens. When the breathing surface is within the body, we discover them again in the tracheae of plants, whose cavity is formed by a spiral fibre that is seemingly intended for some kind of peristaltic motion. We detect them likewise in the pulmonary tubes, in the spiral rings, and in the abdominal movements of insects. We see them in fish swallowing the water and propelling it onward through the fringes of the gills. In the frog, we note them by the motions of the pouch between the sternum and the lower jaw. After this animal is divided transversely behind the fore legs, this pouch continues to fill and to empty itself downwards by the trachea where the lungs were. When the whole integuments and some of the muscles between the jaw-bone and sternum are removed, we see how the pouch was dilated and contracted by a broad cartilage connected with the trachea, and attached by muscles to the inside of the sternum and the neighbouring parts. When the pouch is enlarged, the air rushes in through the two nostrils at that time expanded; and when it is contracting, the glottis starts up with an open mouth to the middle of the pouch, and the air is pressed down through the trachea to the lungs. This amusing sight will sometimes continue for a whole hour. In man and all the warm-blooded quadrupeds, the thorax or cavity where the lungs are placed is dilated and contracted by the diaphragm and muscles attached to the ribs. In the time of dilatation the glottis opens, as we see in birds: the air rushes in, supports the incumbent weight of the atmosphere, and enables the thorax to expand wider. The expanding powers having made at last their usual effort, their antagonists succeed, exert their force, and the air is expelled.
In applying either the water or air to the breathing surface, all these auxiliary organs are assisted by the circumambient fluid which presses equably on all sides. When a Florentine flask is applied to the mouth, and all communication between the larynx and external air entirely cut off, it requires an effort to bring the air of the flask into the lungs. The weight of the atmosphere is therefore assisting in respiration; and the air, whether in the lungs or the thorax (x), must not be so dense as that which is without. When Verheyen perforated the thorax of a dog, and restored the equilibrium betwixt the external and internal air, the respiration of the lungs ceased, though for some time the alternate admission and expulsion of air was continued through canulas introduced into the wounds.
It cannot surely be asked here, how the pressure of the atmosphere should be assisting in raising the thorax, and thus seemingly counteract itself? The heat of the lungs expands the air as soon as it enters. The air rapidly absorbs moisture; and though not usually noticed by philosophers, yet the sudden expansion, which is always the consequence of that absorption, is a very general phenomenon in nature. By this heat, or by this absorption, the air would occasion greater dilatation, were it not for the lungs, which seek to collapse; the cartilages of the sternum, which seek to recoil; and the stretched-out muscles, which either spontaneously, or directed by the will, endeavour to contract and produce expiration.
Having seen how the air will rush in on the opening of the glottis, we may also conceive how the shutting of the glottis will resist the force of internal expansion, and support a weight laid upon the breast. The confined air will expand equally on all sides, and how the pressure must be great before the space which falls expansion to the glottis can exceed its own muscular force and is continued. The diffusion of fluids that produces such striking wonders in hydraulics; and which explains how the dropplings of the ureters should expand the bladder even to a palsy, and overcome the abdominal muscles.
To account for the action of these organs which serve as auxiliaries in respiration, there have been supposed an appetite for air which prompts as a stimulus; an influence of the will, though we breathe while asleep; and a natural instinct, which indeed may exist, but explains nothing. In specifying the several organs concerned, we have heard of an expansive power of the lungs, of a certain pressure of the phrenic nerve, of a muscular diaphragm, and of the action of oblique intercostals. But these explanations are from a limited view of the subject. The expressions used may indeed be general; but their meaning is particular, narrow, and confined; and their allusion is only to man, or perhaps to a few of the warm-blooded quadrupeds: for where are the intercostals of the frog? where is the muscular diaphragm of birds? where the pressure of their phrenic nerve? and where the expansive power of their lungs?
It is fortunate for man that these afflicting respiratory organs are in some measure subject to his will. By this subjection he produces vocal sound when he pleases, divides it into parts, varies it by tones, forms it into words, and enjoys the distinguished and numerous advantages that may be derived from a spoken language.
Sect. II. Digestion.
As respiration succeeded the placenta in one of its offices by maintaining life, the function of digestion succeeds it in another by either continuing or supporting the growth of the living body. It depends on respiration for a portion of heat, and is that function by which the liquid and solid food undergoes its first preparation in the system.
Though gaseous fluids, including the principles of heat and light, may be proved to nourish and compose the substances of all living bodies, yet a part only can enter the system in a gaseous state. This part is of all changed by the lungs, or by those fluids which they contain. The organs of digestion, before they can act on aerial bodies, must have them reduced to some new form. For the food of vegetables, this form requires to be water, whose 100 parts are found to consist of 84½ of oxygen and 15½ of hydrogen. See Water.
(x) Supposing that there be any in the thorax. When the gases have passed through both the watery and vegetable states, they, as juices or solids, become the food of a great many animals. These animals produce new changes, and by their preparation the gases become the food of others which are called carnivorous; and then the carnivorous and all living bodies, when the vivifying principle has ceased within them, and when they are hastening to a state of dissolution, are devoured by others who feed on corruption, are partly converted into water and gas, and become in their turn the food of the kinds on which they had fed.
As these effects of the digesting and assimilating powers are more surprising than any chemical process of art, it may not be unpleasing to take a more particular view of them. It has long been observed, that those animals which are not carnivorous feed upon plants; and, since the days of Van Helmont and Boyle, it has been suspected that plants live upon water and air. This suspicion has now been confirmed by numerous experiments. Plants have been raised from pure distilled water without earth, and instead of requiring a vegetable mould, have spread their roots in moss, in paper, in cotton, in pieces of cloth, in pounded glass, and powder of quartz. From these facts, the ingenious Chaptal has been led to suppose that soil's act but as so many sponges, affording water in different proportions, and in different ways; and that all that the plant wants from the soil is a firm support, a permission to extend its roots where it chooses, and that proportioned supply of humidity which will secure it against the alternatives of being inundated or dried up. To answer, however, these several conditions, he allows it to be necessary in many cases "to make a proper mixture of the primitive earths, as no one in particular possesses them. Siliceous and calcareous earths (he says) may be considered as hot and drying, the argillaceous as moist and cold, and the magnesian as possessing intermediate properties. Each, in particular, has its faults, which render it unfit for culture. Clay absorbs water, but does not communicate it; calcareous earth receives digestion, and gives it too quickly; but the properties of these earths are so happily opposed that they correct each other by mixture. Accordingly we find, that by adding lime to an argillaceous earth, this last is divided, and the drying property of the lime mitigated, at the same time that the stiffness of the clay is diminished. On these accounts it is that a single earth cannot constitute manure, and that the character of the earth intended to be meliorated ought to be studied before the choice of any addition is decided on. The best proportions of a fertile earth for corn are three eighths of clay, two eighths of sand, and three eighths of the fragments of hard stone.
The advantages of labour consist in dividing the earth, aerating it, destroying useless or noxious plants, agriculture and converting them into manure by facilitating their decomposition."
So far is vegetable mould from communicating anything new to plants, that it rather owes its formation to them*, and if sea salt should at times be requisite to marine vegetations, it is to be remembered that salts, fulphur, and lime, are all products of organized bodies; that iron (v) itself has been discovered in plants and animals; and that even diamonds, quartz, crystals, &c., are found only in those earths that begin, are partly composed of an impoverished vegetable residue, which provident nature seems to have reserved for the reproduction or reparation of the earthy and metallic substances of the globe; while the vegetable mould on these organic parts that remain are made to serve as nourishment for the growth of succeeding plants (2).
If those earths in which plants are reared, and which contain no vegetable mould, should ever be sensibly diminished in weight, a circumstance, we believe, which seldom takes place if proper precaution be used to prevent it; yet if it should happen, it should not in that case be forgotten that gases are the general elements in nature; that they mix intimately with the hardest bodies; and that this sensible diminution of weight
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(y) Whether iron exists formally in organized bodies, or is the result of decomposition, it derives its origin ultimately from gases. Blood gradually decomposed by putrefaction yielded not only more salts and lime, but much more iron than blood, suddenly decomposed by lime. Though the greater part of an animal or vegetable, therefore, be without such substances as salt, lime, iron; yet when decomposed its parts may recombine, and thus produce them. See Surgical and Physical Essays, by Mr John Abernethy.
(z) Vegetables in their analysis present us with certain metals, such as iron, gold, and manganese. The iron forms near one-twelfth of the weight of the ashes of hard wood, such as oak. It may be extracted by the magnet. We read in the Journaux de Physique an observation, in which it is affirmed that it was found in metallic grains in fruits. Vegetables watered with distilled water afford it as well as others.
"Beccher and Kunckel ascertained the presence of gold in plants. M. Sage was invited to repeat the processes by way of ascertaining the fact. He found gold in the ashes of vine twigs, and announced it to the public. After this chemist, most persons who have attended to this object have found gold, but in much less quantity than M. Sage announced. The most accurate analyses have shown no more than two grains, whereas M. Sage had spoken of several ounces in the quintal. The process for extracting gold from the ashes consists in fusing them with black flux and minium.
"Scheele obtained manganese in the analysis of vegetable ashes.
"Lime constantly enough forms seven-tenths of the fixed residue of vegetable incineration. Next to lime, alumine is the most abundant earth in vegetables, and next magnesia. Siliceous earth likewise exists, but less abundantly; the least common of all is the barytes. Chaptal's Elements of Chemistry, Part iv. § 3, art. 15.
See Salts, Sulphur, Iron, Lime, in Elements of Chemistry. See the Matrix of Diamonds; see Chaptal, vol. iii. Part 4. § 5, art. 3. Digestion weight may be owing entirely to some dissolution of the solid parts, and the consequent extrication of the gaseous fluids (A).
"Before we had acquired a knowledge of the constituent principles of water," resumes Chaptal, "it was impossible to explain or even to conceive the growth of plants by this single aliment. In fact, if the water were an element, or indecomposable principle, it would afford nothing but water in entering into the nutrition of the plant, and the vegetable would of course exhibit that fluid only; but when we consider water as formed by the combination of the oxygenous and hydrogenous gases, it is easily understood that this compound is reduced to its principles, and that the hydrogenous gas becomes a principle of the vegetable, while the oxygen is thrown off by the vital forces. Accordingly we see the vegetable almost entirely formed of hydrogen. Oils, resins, and mucilage, consist of scarcely anything but this substance; and we perceive the oxygenous gas escape by the pores where the action of light causes its disengagement."
But though water constitute the aliment of plants, we must not suppose that it is the aliment of these alone: the leech and the tadpole* are nourished by water, and many animals have no other food. "Rondelet cites a great number of examples of marine animals which cannot subsist but by means of water by the very constitution of their organs. He affirms, that he kept during three years a fish in a vessel constantly maintained full of very pure water. It grew to such a size, that at the end of that time the vessel could no longer contain it. He relates this as a very common fact. We likewise observe the red fishes which are kept in glass vessels, are nourished, and grow, without any other assistance than that of water properly renewed +."
The ingenious Borelli, who knew that plants and several animals subsist wholly by water and air, was of opinion that some animals lived upon sand. He could discover nothing but sand in the stomachs of many terebraceous animals that live in the water, and particularly in the stomachs of the smaller kinds that live buried in the sand of the sea. He could not conceive what else could be the food of those small fishes or mussels which penetrate the substance of the hardest rocks, and form excavations that always bear a proportion to their bulk. He had regularly found that the why, stomachs of swans which he had examined were full of sand; and, recollecting the pebbles in the gizzards of fowls, he was led to infer that these substances were somehow dissolved in a gastric juice, and served to nourish the harder parts, as the shells, the feathers, and the bones (a). These sentiments, on a slight view, might not be unnatural. From observing children of depraved appetites swallowing sand, ashes, and cinders; from having sometimes met with sand in the stomachs of wild ducks; from the usual feces of the earth-worm; and from the dissection of several toads dug up in a garden, in whose stomachs we could see nothing but a quantity of earth, with pieces of coal, stone, and of flate, that had accidentally happened to be mixed with it (c), we long entertained a similar opinion with this celebrated author: but on recollection
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(A) What follows is from the 33rd additional note of Dr Darwin's Botanic Garden.
"Dr Priestley obtained air of greater or less purity, both vital and azotic, from almost all the fossil substances he subjected to experiment. Four ounce weight of lava from Iceland, heated in an earthen retort, yielded twenty ounce measures of air.
| 4 ounce weight of | Lava | gave 20 ounce measures of air | |------------------|------|-------------------------------| | 7 | Basalt | 104 | | 2 | Toadstool | 40 | | 1 1/2 | Granite | 20 | | 1 | Elvain | 30 | | 7 | Gypsum | 230 | | 4 | Blue slate | 230 | | 4 | Clay | 20 | | 4 | Limestone spar | 830 | | 5 | Limestone | 1160 | | 3 | Chalk | 630 | | 3 1/2 | White iron ore | 560 | | 4 | Dark iron ore | 410 | | 1 1/2 | Molybdena | 25 | | 2 | Stream tin | 20 | | 2 | Steatites | 40 | | 2 | Barites | 26 | | 2 | Black wad | 80 | | 4 | Sandstone | 75 | | 3 | Coal | 700 |
"In this account the fixed air was previously extracted from the limestones by acids, and the heat applied was much less than was necessary to extract all the air from the bodies employed."
(b) A similar inference was made by Mr Burt upon opening the stomach of the pangolin of Hindostan. See Pangolin.
(c) The third ventricle had a strange body fastened to its interior membrane. This body was composed of a hard membrane, in which there was gravel inclosed. Gesner says the chamois is accustomed to swallow gravel to clear his tongue and throat from the phlegm, which is apt to cover them, and destroy the appetite. Anat. Description of the Chamois or Gemp, by the French Academy." ing that many substances which enter the stomach are not nutritious; considering the balls of hair and of feathers which the carnivorous animals return, and that quantity of fecal matter which is discharged by the intestines; having frequently experienced that a sense of fulness removes hunger, and observed persons as it were by instinct pressing on the empty stomach with their hand—we began to suspect that the swallowing of sand, and a number of other indigestible substances, might not be to nourish but to prevent some cravings of the stomach, and that these cravings were in part occasioned by a deficiency of the usual pressure which it receives from the neighbouring parts. In this opinion we were more confirmed, by hearing it was customary among some of the tribes of the north of Asia to repel or mitigate the attacks of hunger by placing a board over the region which is called epigastric, and compelling it gradually by means of cords as the stomach collapses; and by learning afterwards, on a further inquiry, that a similar practice, and from similar motives, was likewise common with some individuals in this country; who, to alleviate the sensation of hunger, straiten the epigastric region with their handkerchief. This practice, however, being often impossible with the brute kind, instead of bringing the neighbouring parts to press on the stomach, they are obliged to distend the stomach, and to bring it to press on the neighbouring parts. Of the two ways of producing this pressure, the last is certainly the most natural. Senecio has supposed that distention of the stomach is the cause of the secretion of the gastric liquor; but how well or ill his opinion may be founded, daily experience permits not a doubt, that, in order to satisfy the calls of hunger, the stomach requires not only to be nourished, but to be filled, or at least to have something like a sense of fulness; and this may probably be one reason for those balls which are found in the stomachs of the chamois, which likewise swallows sand, and in the stomachs of the cow, the sheep, and of the horse, "when they do pass away the winter in snowy mountains, where they can find no grass" (d).
From this general view of the food, the natural transition is to those organs by which it is prepared. As all plants are fed on nothing grosser than liquids, we see the reason why they are all nourished by absorbents, and why, instead of one common alimentary canal, they are furnished with a number of capillary vessels, which by their action assist the living power in moving the fluids along the trunk, the branches, and the leaves.
These fluids are observed to move between the different ligneous circles, and the more copiously as the wood is younger or the nearer the circles are to the bark. In the circles themselves, it has been remarked that the sap vessels, from being empty during a great part of the growing season, have been called air vessels; that they are formed of spiral fibres, adapted to some peristaltic motion (e); and it is plain, that by this structure they are well fitted to propel their contents, whether water or air, upwards or downwards, backwards or forwards, according to the different positions of the plant.
Besides the particular action of the vessels, a general concurrence is received from the movement of the water or winds, which serves as an exercise; a general promoted dilatation is occasioned by both moisture and heat; and a general contraction by dryness and cold, which produce a motion something similar to that of the thorax (f).
In the springing season the sap ascends through the empty vessels before the leaves begin to appear. When the vessels are filled through their whole extent, the buds swell, the leaves spread, and the flowers blow; the evaporation from the surface is increased; the sap is diminished by the absorption; the succiferous vessels now cease to bleed (f); and the roots being unable to supply the waste, the rains and the dews enter by the trunk, the branches, the leaves, and the petals of the flowers. When the evacuations are immoderately increased by excessive heat, or preternaturally obstructed by moisture by the plucking of the leaves, by too much humidity, in the vegetation, or other causes which prevent perspiration, the plant soon either sickens or dies. The chyle, which is formed in the sap vessels, has generally something of a saccharine taste.
Considering the forms of animal food, we may naturally expect in the animal kingdom a greater variety of those organs employed in digestion. Most animals have indeed, like the vegetable, both inhaling and exhaling vessels, by which some of their fluids are absorbed, and evacuations regularly carried on. Except, however, in those animals which subsist by liquids, these vessels are of little importance in receiving food or ejecting what is useless from the system. In these animals the absorbents terminate in a hollow viscus, which is called the alimentary canal, where the fluids undergo a preparatory change, and are partly reabsorbed for assimilation. In all others the food enters by a proboscis (g), or by an aperture which is called the
(d) Bartholine, quoted by the French Academy, thought that these balls were composed of the hair which the cows lick from their skin, or of the wool which the sheep eat. But the horse does not lick himself, and many of these balls seem to be composed of ligneous fibres. The balls which are found in the chamois are called by Vesalius German bezoor. See Anat. Description of Chamois or Gemp, by the French Academy.
(e) "The superior part of the intestine, which contained about thirteen inches, had a very particular structure; for, instead of the ordinary circumvolutions of the intestines, the cavity of this was transversely interrupted with several separations, composed of the membranes of the intestine folded inwards. These separations were near half an inch distant from each other, and turned round like the shell of a snail or of a staircase with an open newel." Anat. Description of the Sea-fox, ibid. These membranous folds running spirally, are not uncommon in the alimentary canals of animals.
(f) This happens in a great many plants.
(g) Every person may have an opportunity of seeing a proboscis in a number of those winged insects which extract juices from plants. It is very easily discernible in the butterfly. In this insect it is a fine moveable tube.
This in the parrot was observed by the gentlemen of the French academy. It has since been observed in rooks, macaws, cockatoos, and others; and Mr Hunter, to whom physiology is so much indebted, discovered, that the male and the female pigeon secrete in their inguivies a certain liquor for feeding their young birds, and that most kinds of what have been thought ruminating birds do very often in expressing their fondness regurgitate their food. Yet both this and another species of regurgitation which is very common with those animals that swallow indigestible substances with their food, should be carefully distinguished from rumination.
To the ruminating kinds the diluting sac is by no means peculiar. The porpoise has one, though it does not ruminate; and many of those animals which have none, as the rat, the hog, and the horse, have a part of the stomach covered with a cuticle, and which must therefore principally serve as a reservoir. The gullets of several fishes and serpents are sacs of this kind. It frequently happens that a part of their prey is projecting from the mouth, while another part fills up the gullet and gradually descends, to be reduced in the following below. So very dilatable are the stomachs and gullets of some animals, that serpents have been often seen to swallow whole animals which, prior to the gorging, were larger than themselves; and many poultries, and even some of the loupe kind, will, by swallowing food, more than double their own bulk.
Applying stomach as a general word to the different number of ventricles of the canal, we may here observe, that every stomach species of animals which ruminate have two stomachs, or at least two divisions in one; that some have three, as the gazelle; and some four, as the cow, the dromedary, and the sheep: but it must not be supposed that the number of stomachs is any proof of a ruminating power. It was said already that the porpoise has two; the porcupine has three divisions in one; and the singular cafflaw, although it be found to have four stomachs, does not rumi-
tube, possessing a great variety of action. It serves for a hand, a mouth, and a gullet; and when not extended in search of food, it is coiled up in circular folds. The elephant has both a mouth and proboscis, and this proboscis is one of the most singular of living organs.
(h) The crocodile has no tongue; the ostrich, the seal, and some others, have forked tongues; the cormorant has a double tongue; some, like the eagle, have a cartilaginous tongue; some, like the porcupine, have it toothed. We have found a bone in the tongue of a goose; the tongue of the camelion is a hollow trunk like a proboscis; the tongue of the frog is forked and long—it is rolled up in the mouth, and originates from the fore-part of the lower jaw. In some the tongue is the organ of taste; in others, the instrument for seizing their prey. In distinguishing foods most animals rely chiefly on smell.
(i) These instruments are cornaceous, bony, or calcareous; they are teeth or bills; their situation is the tongue, the jaws, the palate, or the stomach. Many teeth seem intended only for attack or defense, for seizing, killing, or retaining the prey. This is remarkable in the fans of serpents, and in the large tusks of the elephant, the barbieroussa, and some other animals, where they have some resemblance to horns, and project from the mouth. The philodotus and ant-eater have no teeth; the larvae of insects have generally two, which are placed externally, and cut like a forceps.
(k) There are many persons whose tongues and mouths are naturally dry, and when they swallow a piece of bread must call for water or some other moistener. This complaint is even sometimes general in a family, and is propagated like an hereditary evil through its different branches. Cockatoos and parrots have likewise dry mouths.
(l) The buffard has no sac of this kind; but the oesophagus is remarkable for the largeness of its glands.
(m) In the ostrich the oesophagus passes down and returns, and the crop opens from below upwards into the gizzard.
Digestion, ruminate; nor, although granivorous, is any one of the four a gizzard.
Somewhat different from these expansions which we have been mentioning as existing in the first part of the alimentary canal, is a sort of pouch (n) which hangs from the neck and the lower mandible of several birds, and which, like the two pouches of apes, may be used either to macerate the food or to carry provisions from a distance to their young. The pelican, a native of warm countries, employs this pouch sometimes to carry a quantity of water; and another native of the same countries, we mean the dromedary, was observed to have at the top of the second of the four ventricles a number of square holes, which being the orifices of as many cavities between the membranes which compose the ventricle, reminded the gentlemen of the French academy of those large reservoirs of water, which Pliny mentions to be in camels; and for which, according to his story, their guides have opened them sometimes in cases of extreme thirst.
We come now to one of the principal agents in digestion. Independent of the fluids which mingle with the food in the mouth, the gullet, or macerating sacs, there is one denominated the gastric juice, and which, either by itself or along with others from the aliments which it contains, acts in some measure as a solvent. It is secreted from large glands at the entrance of the gizzard, from vessels or glands in the coats of the stomach, and perhaps most plentifully near the pylorus; it powerfully retards the putrefactive fermentation; it coagulates milk and the white of an egg; it dissolves food even when inclosed in metallic tubes; and when life ceases, it acts frequently on the very stomach from which it was secreted. Its taste, its colour, and its solvent powers, are different in different classes of animals. It seems to be modified according to the age, the health, the habit, and the different aliments on which they live. The sick and the child are incapable of digesting the food that is proper for a healthy man. The hawk kind, after loathing bread and throwing it up without any change, can be gradually brought to take it for food; and Gassendi has mentioned a certain lamb which, being fed on bread, cheese, and on flesh, refused afterwards to taste grass. But what is most surprising in the gastric juice is, that it spares all living bodies, as those worms which exist in the stomach, and the stomach itself while it is alive; and it differs otherwise from a chemical solvent, in that it has an assimilating power, and reduces all substances, whether animal or vegetable, on which it acts, to a certain fluid of determinate properties, which is called chyle.
Besides the gastric, the food again, after passing through the stomach, is mingled with a greenish fæcalaceous liquor, which is called bile, and which flows either immediately from the liver or from a vesicle into which it had regurgitated as into a blind gut; at the same time nearly it is mingled with another resembling the saliva from the pancreas or sweet bread; a gland or glands whose place is supplied in a great many fishes by a number of vermicular appendages to the digestive stomach.
In short, from one extremity of the alimentary canal to the other, fluids are perpetually flowing into its juices, cavity from glands, vessels, or organic pores; and the membranes constantly secreting a mucus to protect themselves from the acrimony of their contents. This acrimony must often be considerable near to that end of the canal where the feces are discharged; for as the first part of the canal has generally one or more dilatations which are called stomachs, and secretes at least one fluid which is strongly antiseptic, so the last part has generally appendages which are called cæca, where the food always remains for some time, and where, from the air, the quantity of animal matter that happens to be mixed, mingled with it, becomes putrefactive. The office of the cæca is sometimes supplied by the largeness and convolutions of the colon(o); to which gut the ileum cannot, when it enters laterally, so easily communicate its peristaltic motion. As the stomachs were the receptacles of the food when it entered, the cæca are receptacles of the fecal matter before it be discharged. They are of various forms and capacities; they are often larger than the stomach itself; are often composed of proportionally thin and transparent membranes; and from their contents have often a colour somewhat resembling that of the gall-bladder. Their number is different in different animals. Some have but one. The birds which have them have generally two; the bustard has three; and Swammerdam has dissected insects which had four. As some stomachs have a number of folds which hang pendulous within their cavity, and increase their surface, so have often the cæca as well as some portions of the canal. The cæcum of both the rabbit and the hare is curiously formed. It is large and beautiful; it is rolled up like a cornu ammonis; it has the like outward appearance; and a fold running spirally is observed within. The animals which live on vegetable food have usually the greatest length of the canal, and the greatest number of stomachs and of cæca: yet the cæcifow, which has no gizzard, has no cæcum; and the polype, which is said to be all stomach, is properly speaking rather all cæcum.
To see more fully the process of digestion, we must not overlook that general and organic action which the aliment takes place through the whole alimentary canal. The power of mastication exerted in the mouth is obvious to all. But the force of some stomachs has till very lately been known to few; we allude here to that of the muscular or gizzard kind: for Alibé Spallanzani has divided stomachs into three sorts; the muscular, the membranous, and intermediate. The immortal Borelli, who was probably the first that tried the force of the muscular stomach, by throwing into them nuts, stones, seeds, hollow spheres of glass, hollow cubes of fish, lead, small pyramids of wood, and several other very mated by hard substances, supposed that the power exerted by the stomach of the Indian cock(p) was equal to 1350 pounds.
(n) A pouch of this kind is observed in our common rook. (o) The bear, whose intestines are 40 feet long, has nothing resembling a colon or a cæcum. (p) The original is gallus Indicus, which in the writings of Longalius, Gesner, and Aldrovandus, means a bird. pounds weight. The force of an intermediate stomach cannot be so great, and that of a membranous one must be still less. Each seems to have more of the solvent as it has less of the muscular power. The most membranous are assisted by the action of the neighboring parts, and expel their contents as readily as the strongest. The muscular sort is either wholly or principally confined to certain kinds of birds and of fishes, as nature has meant that the grain or the shells which they use as food should first be triturated before it be subjected to the gastric juice. This comminution takes place in their stomachs, because it is plain that had bones or mucles, fully equal to all these effects, been placed in the head, the form of the animal must have been altered, or that equilibrium which it preserves in those fluid elements through which it moves been completely overturned.
As to the movements of the alimentary canal, the direction of hairs found in the stomachs, and the balls of hair which are thrown up, would appear to indicate a circular motion. The intestinal part has a motion similar to that of a worm, and is called the vermicular or peristaltic. Here every portion retains its own motion, although it be separated from the rest by ligatures. The stomach of the polype, the gullets of the ruminating kinds, and the coeca, have this motion in different directions at different times; and that observed in the alimentary canal of a loupe is, when viewed through a microscope in the time of action, amazingly rapid; the stimulating causes employed are the food, the different liquors with which it is mixed, the air, the nerves where they exist, and a portion of heat. Some degree of heat is necessary to every process of digestion both in the animal and vegetable kingdom; what that degree is depends on the nature of the living body; and is various according to its age, its health, its employments, and habits. The ingenious Hunter has mentioned the digestive and generative heats; and those gardeners who are versant in the operations of hot houses, have on their thermometers the swelling, flowering, and the ripening heats, with a great many others for the several plants which they mean to raise.
Among the other causes of digestion some authors have ranked fermentation; and it must be allowed, acetic, and that something similar to the putrefactive fermentation takes place in the coeca and the lower extremity of the intestine, and that the vinous and acetic fermentations but too frequently occur in our stomach when that viscus is morbidly affected (a).
Much of the history of living bodies relates to the different degrees of heat, the varieties of soil, and the cestry to-kinds of food concerned in digestion. The plants grow where the soil and the heat are congenial to their nature; and those which admit of the greatest variety with respect to soil, and the largest range on the
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bird different from the coq d'Inde or Turkey cock. Johnston has called it gallus Persicus. See The Anatomical Description of two Indian Cocks by the French Academy. Gallina Indica is Ainsworth's Latin for the Guinea hen. See Borelli de Nutrit. Animal. Prop. 189, 190, 191.
(a) "It may be admitted as an axiom (says Mr Hunter), that two processes cannot go on at the same time in the same part of any substance; therefore neither vegetable nor animal substances can undergo their spontaneous changes while digestion is going on in them; a process superior in power to that of fermentation. But if the digestive power is not perfect, then the vinous and acetic fermentation will take place in the vegetable and the putrefactive in the food of those animals which live wholly on flesh. The gastric juice therefore preserves vegetables from running into fermentation and animal substances from putrefaction; not from any antiseptic quality in the juice, but by making them go through another process, prevents the spontaneous change from taking place.
"In most stomachs there is an acid, even although the animal has lived upon meat for many weeks: this, however, is not always the case; therefore we must suppose it is only formed occasionally. Whether the stomach has a power of immediately secreting this acid, or first secretes a sugar which afterwards becomes acid, is not easily ascertained: but we should be inclined to suppose from analogy the last to be the case; for animals in health seem to have the power of secreting sugar, as I find in the milk, and sometimes in the urine from disease. The acid prevails sometimes to a great degree as to become a disease, attended with very disagreeable symptoms; the stomach converting all substances which have a tendency to become acid into that form: the sugar of vegetables, and even sometimes vinous spirits, turning directly into acid.
"To ascertain whether there is an acid naturally in the stomach, it will be proper to examine the contents before the birth, when the digestive organs are perfect, and when no acid can have been produced by disease or any thing that has been swallowed. In the flint calf, near the full time, there is acid found in the stomach, although the contents have the same coagulating powers with those of animals who have sucked.
"Spallanzani gives the opinion of authors respecting digestion; and so anxious is he to combat the idea of its being fermentation, that he will hardly allow that fermentation ever takes place in the stomach. That fermentation can go on in the stomach, there is no doubt. It is often found that milk, vegetables of all kinds, wine, and whatever has sugar in its composition, become much sooner sour in some stomachs than they would if left to undergo a spontaneous change out of the body; and even spirits in certain stomachs almost immediately degenerate into a very strong acid. All oily substances, particularly butter, very soon become rancid after being taken into the stomach; and this rancidity is the effect of the first process of the fermentation of oil. Mr Sieffert has been able to restore rancid oils to their original sweetness, by adding to them their due quantity of fixed air; the loss of which I consider as the first process in this fermentation, similar to what happens in the fermentation of animal and vegetable substances." Observations on Digestion by Mr Hunter. the scale of heat, are the farthest dispersed over the globe. As every soil has usually some regular supply of moisture, the plants that can live upon that supply extend their roots under the surface where their liquid food is the least exposed to evaporation, and meeting there with the constant nourishment which they require, they remain in that situation for life (a). If their trunks be so feeble as to need a support, they creep on the ground, they climb the face of a neighbouring rock, or cling to the loly of some of the statelier children of the forest. Their range for food is extremely limited; it is chiefly confined to the small space which happens to be occupied by their roots and branches; yet if any uncommon exertion be necessary, the branches will bend, and the leaves turn to drink of the water that is passing by. If the roots be laid bare, they will again plunge into the earth; if a stone or a ditch be thrown in the way, they will move round or will dip downwards, and spread into the soil on the other side; if there they arrive at one that is unfriendly, they will not enter; but if a favourite earth should be near, though not in their direction, they will twirl about, advance as they grow, and at last meet it. In all these cases the prop, the water, and soil, must be necessary; they must also be within a very small distance, otherwise the plants cannot perceive them, or will fail in their languid attempts to approach them.
It may be considered as a general fact, that wherever food is liberally supplied for a whole lifetime in one place, the creatures which use it have seldom much locomotive power, or much inclination to exercise it in a long continued and progressive line. The curious insect is therefore observed to deposit its offspring in those places where the prospect of genial warmth and of plenty seem to preclude the future necessity of wandering or research; and when this offspring is about to pass into a new state, and the organs foretell that a change or perhaps a variety of food will soon be required, the appearance either of wings or of legs do likewise forebode that the power of locomotion is to be increased. Even noisier animals in their fatal state, where they live upon one species of food, and where that is afforded in regular plenty, do spread out their roots, adhere to their soil, and become as stationary as the plant itself; and even when that supply is withdrawn, and they are expelled, yet if the state into which they emerge be helpless and feeble, if their organs of digestion have a weak solvent or masticating power, particularly adapted to some easily assimilated food, and if that food be presented either by their parent or nature without their exertion, their powers of locomotion is not great, nor is it exercised in wandering afar. It is when the organs of digestion are strong, and the appetite inclines to variety of aliment, that they are disposed and feel themselves able to wander in search of it; and that then they may be ready to move at intervals from place to place, when the enemy comes or the spirit prompts them, nature has directed them to solid food, and has given them a large alimentary canal with stomachs, with convolutions, and coeca, where they may lay up provisions for a journey; but afraid to entrust them with too much freedom, left in their excursions they might wander from the places where subsistence is found, there are two appetites, hunger and thirst, which never fail in a state of health to remind them of their duty.
This variety of food, and the manner in which it is affected by climate, are the cause of the many and singular migrations from spot to spot, from country to country, and from sea to sea: they are the cause of some kind of torpor in the hedgehog and the bear, and they partly explain the provident foresight of the ant and of the torpid bee. Animals of great locomotive power, in order to provide for themselves and their offspring, remove to a distant country or climate when they see the signs of approaching famine. Those of less locomotive power, and who are incapable of migrating far, as if warned by heaven, lay up a store for the scarcity to come; or should their food be of that kind as not to be easily preserved for a season, they receive no secret warning to hoard it at the time when it fails, their system becomes susceptible of torpor, and they are enabled to sleep through the storm of trouble and of want. The source of this want is in most instances to be traced to the nature of the plant and insect. The plant which has little heat of its own depends on the sun or some other agent for one of the great causes of digestion. When this agent refuses the necessary heat, the plant must decline; its leaves, its juices, and its fruits must fail. The insect tribe, which had no other food, or which like the plant could not maintain their vivifying warmth, must likewise submit to the same fate. The various animals which live on either the one or the other, according to their several dispositions and characters, retire to their stores, to their dens of torpor, or migrate to a country to which they are led by unseen guides to share in its abundance. Of these last the rail (s) and the swallow are the only two which are sometimes arrested, and which, with the bear, the hedgehog, and the toad, are obliged to remain in the dwellings of torpor till the genial season of warmth and of plenty.
Sect. III. Absorption.
When the food has undergone the first preparation, which is called digestion, and the chyle (t) is formed in the
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(a) Many of the fat plants live chiefly by the absorption of moisture from the air; and many sea-plants float through the ocean, and having plenty of food wherever they go, they send out no roots in order to search for it.
(b) All the birds on the lakes of Siberia are said by Professor Gmelin to retreat southward on the commencement of frost, except the rail, which sleeps buried in the snow. Account of Siberia quoted by Dr Darwin in his *The Loves of the Plants*.
(c) The chyle of different living bodies has not yet been analysed; in man it is generally a whitish fluid resembling milk, and yielding water, oil, sugar, and a coagulable lymph. Absorption, the alimentary canal or sap-vessels, it is thence taken up by means of absorption for the use of the system. From the vessels it passes into the whole cellular tissue, composed of vehicles, and closely interwoven with all the vascular part of the plant. From the vehicles or utricles of the cellular tissue it enters the vasa propria and glands, which contain and prepare the fluids and secretions peculiar to the species.
In animals, the lacteals veins spreading on the gut, till the 1622, when Afellus an Italian discovered the lacteals (v) running on the mesentery of a living dog, and printed his account of them in 1627. As he had not traced their course very far, he naturally thought that they went to the liver, which was then imagined to be the organ of sanguification. This opinion, with respect to the place where they entered the veins, continued to be general till 1651, when Pecquet in France published his account of the thoracic duct (x). With great candour this author acknowledged, that he had been led to make the discovery by observing a whitish fluid mixed with the blood in the right auricle of the heart of a dog, which kind of animal it had been customary to dissect alive since the time of Asellus. "This practice of opening living animals furnished likewise occasions (says Dr Hunter) of discovering the lymphatics. This good fortune fell to the lot of Rudbeck first, a young Swedish anatomist, and then to Thomas Bartholinus (y) a Danish anatomist, who was the first who appeared in print upon the lymphatics. His book came out in 1653, that is, two years after that of Pecquet; and before Vol. XIV. Part II.
(v) We learn from Galen, that the lacteals in kids had long before been seen by Erasistratus, who called them arteries.
(x) This duct had been seen before by Eustachius. See Eustach. de Vena sine pari.
(y) The discoveries of Rudbeck and Bartholinus were made in the years 1651 and 1652, about which time Jolyffe an Englishman saw also the lymphatics.
(z) Drs Hunter and Monro claim the merit of having found out the true use of the lymphatics. The former says that he taught it in his lectures so early as 1746, and appeals to his pupils for the truth of the assertion. The latter seems to have made the discovery in 1755; and in 1755 published an account of it in a thesis De Tofibis in variis Animalibus. Before the printing of this thesis, Dr Black told him that the same opinions concerning the valvular lymphatics had been long entertained by Dr Hunter. In 1756 Dr Monro attended Dr Hunter's lectures in London; heard the whole doctrine of the lymphatics very fully explained; and in 1757 reprinted his opinion at Berlin without taking notice of Dr Hunter's, who charges him with plagiarism; and the charge is retorted by Dr Monro.
(a) Lymphographiae, quod offertur specimen, ubi lectori non ingratum percepero ad alias transiturus tum partes, non minus quam haec, lymphaticis ductibus superientes. Prefatio ad Adenographiam.
Nuck had traced lymphatics on the exterior parts of the head and neck, on the membrane of the lungs, on the spaces between the ribs, in the loins, on the diaphragm, on the heart, the spleen, on the liver, the gall-bladder, on the stomach, on the mesentery, on the tunica albuginea of the testes, in the feet, and in the hands. Ita (continues he), ut multiplex experientia et variis partium preparationibus eo usque pervenerim ut integrum lymphaticorum systema a capite ad calcem mihi componerim, cujus delineationem libenter teorem communicato, ubi partium nonnullarum haecenum nondum satia examinatarum, Lymphographiam absolverimus. Anton. Nuck de Inventis novis Epistolae Anatomica ad D.D.B.G. Mod. Doct.
(b) Quidam nervos constituentis vasorum lymphaticorum principia; ali glandulas minores; ali mem' ranas; nec deficient qui a tendinofa musculorum parte eadem deducant. Sed niflis aliorum sententias, dicam modo; varia me hanc circa speculationem molitum fuisse, varia experimentis (irrito licet ordinariorum conatu) varia tentaties, eisque tandem nonnulla extelesse qua lucem, hic adterre possunt.
Ante triennium, mundando lien vitulino intentus, omnique sanguine, aquae tepicæ ope, jam eloto, copiosum in arteriam splenicam infundi aerem, et, spiritu fortius adacto, non tantum plurimas exiguas in superficie lienis vidi elevari vehicules, sed ex illud vehiculis vasa prodire lymphatica, statu etiam turgida et liemen perrepantia vidi, et quo diutius arteria fuit inflata, eo majorem notavi vasorum numerum, ita ut, hac arte per inflatum the founder opinion of Glisson, of Hoffman, and some others, the old notion that the veins performed the office of absorbents came so far down as the great names of Haller and of Meckel. The arguments, however, by which it was supported are known now, and particularly by those of the Hunterian school, to have been injections that were not skillful, observations that were not accurate, and conclusions that were not logical; while the boasted assertion that birds and fishes were without lacteals and without lymphatics, has been disproved by the fortunate discoveries of Mr Hewson and Dr Monro. Excepting, therefore, in the penis and placenta, and in those animals whose veins may be injected from the gravid uterus, the lymphatics seem to perform the whole business of absorption. They contain a fluid that is coagulable like the lymph of the blood, and are called valvular to distinguish them from the arteries that do not admit the red globules. They derive their origin from the cellular membrane, from the different cavities, and from the surface. Some authors say that they have seen them in the brain (c), and the Mafagni has ventured even to describe in prints. That some indeed may exist in the brain, has not been denied; but to believe that they have been found, and to trust assertions which are not countenanced by the observations of skilful anatomists, requires a faith which for our part we do not pretend to. Both they and the lacteals derive their name from the colour of the fluids which they contain. They both empty themselves into the veins; but most of the lymphatics in the human subject, and all the lacteals, first unite in the thoracic duct, which near the heart leads into the course of the circulation.
Sect. IV. Circulation.
After part of the food is converted into chyle, and this chyle absorbed by the lacteals, and brought into the course of the circulation, it remains to be distributed to all the different parts of the system. On this account, Hippocrates speaks of the usual and constant motion of the blood, of the veins and arteries as the fountains of human nature, as the rivers that water the Hippocratic whole body, and which if they be dried up man dies. He says that the blood vessels are for this reason every where dispersed through the whole body; that they give spirits, moisture, and motion; that they all spring from one; and that this one has no beginning and no end, for where there is a circle there is no beginning (d). In such language was the prince of physicians accustomed to express his vague ideas of a circulation; so far was he from having acquired accurate conceptions on this subject, that when he saw the motions of the heart, he believed that the auricles were two bellows to draw in air, and to ventilate the blood.
When after his time anatomy came to be more studied, the notions of the ancients respecting the blood were better defined; and, however chimerical they may have seemed to us, they were partly derived from dissection and experiment. On opening dead bodies, they found out blood that the arteries were almost empty (e), and that very in dead nearly the whole of the blood was collected in the bodies, veins, and in the right auricle and ventricle of the heart. They therefore concluded that the right ventricle was a sort of laboratory; that it attracted the blood from the Cave; by some operation rendered it fit for the purpose of nutrition, and then returned it by the way that it came. From the almost empty state of the arteries, they were led to suppose that the right ventricle prepared air, and that this air was conveyed by the arteries to temper the heat of the fever. To this last notion entertained by Erasistratus, Galen added an important discovery. By certain experiments, he proved that the arteries contained blood as well as the veins. But this discovery was the occasion to which the branches of the veins were distributed.
To this last notion entertained by Erasistratus, Galen added an important discovery. By certain experiments, he proved that the arteries contained blood as well as the veins. But this discovery was the occasion to which the branches of the veins were distributed.
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(c) Sed rogare videtur, utrum in cerebro etiam vasa occurrent lymphaticia? Quamvis ex recentioribus observationibus, systematis in proprio cerebro formant et vescera ex su placeru componunt: ad experimenta enim provocati nihil egregii praetere valent. Nunquam hac in parte, ut ingenue loquar, hactenus Scopum attingente potui. Interim non negandum censo aliquando cerebri lymphatica in una aut altera parte suffisse visum; et non ita pridem, anatomicus quidam mihi acerrimus, inter alia inventa, haec nobiscum communicat. "Vidi, inquit, lymphaticum in cerebro Bovino, quod examine tuo (ut originem facias et insertionem) erit dignissimum. Non longe a glandula pineali, qua ramos forte habet, incumbit plexui choroidaeo, ad infundibuli latera se extensum." Ante biennium ductum lymphaticum ex pini glandula codem modo ut aliis glandulis, exexunt vidi. Ita ut quidem certissimum, et cerebrum suos habere rivulos aquosos, sed nondum distincte, in lucem protractos.
(d) Hippocr. de Venis. "Plato, in his Timaeus, speaks of the heart as a watch-tower completely fortified, as the knot of the veins, and the fountain from whence the blood arises, and briskly circulates through all the members. The blood he calls the pasture of the flesh; and adds, that for the sake of nourishing the remotest parts, the gods have opened the body into a number of rivulets like a garden well stocked with plenty of canals, that the veins might by this means receive their supply of moisture from the heart as the common source, and convey it through all the sluices of the body." The rest of the passage cited by Longinus is as full of nonsense as it well can hold: and indeed Longinus seems chiefly to have admired it for something which had struck him as divine and unparalleled in its tropes, as making the head a citadel, the neck an isthmus, the vertebrae hinges, and the flesh a rampart. See Longinus on the Sublime, § 32.
(e) Erasistratus opened dead bodies at Alexandria. of some embarrassment. How was the blood to get from the right to the left ventricle? To solve the difficulty in which his new discovery had involved him, he supposed that the branches of the veins and arteries anastomosed (r); that when the blood was carried to the lungs by the pulmonary vein, it was partly prevented by the valves from returning; that therefore during the contraction of the thorax it passed through the small inofculating branches to the pulmonary vein, and was thence conveyed along with the air to the left ventricle to flow in the aorta (g). This opinion, so agreeable to fact, unfortunately afterwards gave place to another that was the result of mere speculation.—This notion was, that the left ventricle received air by the pulmonary vein, and that all its blood was derived through pores in the septum of the heart.
The passage thro' the septum being once suggested, and happening to be more easily conceived than one thro' the lungs, it was generally supposed the only one for a number of centuries; and supported likewise, as it was thought by Galen's authority, it was deemed blasphemy in the schools of medicine to talk of another. In 1543, however, Vesalius having published his immortal work upon the structure of the human body, and given his reasons in the fifth book why he ventured to dissent from Galen, he particularly showed how it was impossible that the blood could pass through the septum of the heart. His reasoning roused the attention of anatomists; and every one grew eager to discover the real passage which the blood must take in going from the right to the left ventricle. The discovery of this fell first to the lot of Michael Servetus, a Spanish physician, who published his opinion, and refuted by Vesalius.
Vesalius roused the attention of anatomists to discover the true passage of the blood between the ventricles. It appears by his peripatetic questions printed at Venice in 1571, and reprinted there with his medical questions in 1593, that he knew not only the lesser circulation, but had observed that there were times when the blood flowed from the branches of the veins towards their trunks, and that veins swelled between their ligature and the extremities, and not between the ligature and the heart. From these observations, he necessarily inferred that the veins and arteries anastomosed; and having also contemplated the whole nature of all the valves which were then known, and circulation had been known since the days of Galen, he ventured very nearly to assert that the blood could not return by the arteries to the left ventricle. One should imagine that from such firm conclusions he must have discovered the true circulation; but he did not. Being a zealous peripatetic, he thought himself bound to maintain with Aristotle that the blood flowed, like the tides of Euripus, backwards and forwards in the same channel; and therefore supposed that it flowed from the arteries into the veins in the time of sleep, and from the veins back into the arteries in the time of waking. The greater circulation, so far as we can learn, was not even dreamed of by this writer. A farther step was yet to be made towards its discovery; and this was reserved for another professor of the Paduan school.
In 1574, Hieronymus Fabricius ab Aquapendente, while he was seeking for a cause to explain the varicose swellings of some veins which had arisen from friction and ligature, he to his great joy and astonishment discovered their valves in one of his dissections; and henceforth the true theory of circulation seemed almost unavoidable. Yet whoever reads the small treatise De Ve- nariis (folia), first printed by Fabricius in 1603, will soon perceive that he was as far from entertaining a just notion of the circulation as his predecessors. Notwithstanding all that he saw, he still was of opinion that the blood flowed from the heart to the extremities even in the veins. He thought that the valves were intended by nature only to check and moderate its force. He calls them an instance of admirable wisdom, and mistakes his own awkward conjecture for one of the designs of infinite intelligence. In another respect, it must be confessed that he bore no inconsiderable share in promoting the discovery of the circulation (i). By writing on the valves, the formation of the fetus, and the chick in ovo, he directed the attention of his pupil Harvey to those subjects where it was likely that the motion of the blood would frequently occur.
Harvey was born at Folkestone in Kent in 1578, completed his studies at the university of Cambridge, and fully went to Padua, and was there admitted to the degree of doctor, with unusual marks of approbation, in 1602. He examined the valves with more accuracy than
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(f) In toto est mutna anastomosis atque ofculturum apertio arteriae simul cum venis. De Utn, part 6. cap. 10.
(g) It was the opinion of Galen, that the motion of the lungs and the pulse of the arteries was to cool the blood, and to expel the fuliginous vapour. That he had just ideas of the lesser circulation through the lungs, and of the true nature of the valves, is evident from the passages cited by Harvey, De Motu Cordis, Exercit. 1. cap. 7.
(h) The words in which he mentions this discovery are these: "Non per parietem cordis, ut vulgo creditur, sed magno artificio ad dextro cordis ventriculo, longo per pulmones ductu agitatur fangus subtilis." Being born at Villa Nuova, in the kingdom of Arragon, he sometimes called himself Michael Villanovanus, or simply Villanovanus. In the title of all his books he takes the name of Rewer, which is formed from Servetus, by throwing out the de and transposing the five letters that remain. The book in which his discovery was mentioned was printed clandestinely, and intitled Christianitas Restored. Being first imprisoned at Vienna in Dauphiné, and afterwards allowed to Geneva by the treachery of his correspondent and confidant John Calvin, he was, by a servant of that reformer's, accused of blasphemy, and condemned to the flames in 1553.
(i) Almost the whole merit of his discovery is due to the Paduan school, of which Cesalpino as well as Columbus was once a professor. than his master Fabricius; and explained their use in a treatise which he published some time after. It is uncertain when he first conceived his celebrated doctrine of the circulation; but about the 1616 he taught it in his lectures, and printed it in 1628. He was the first author who spoke consistently of the motion of the blood, and who, unbiassed by the doctrine of the ancients, drew rational conclusions from his experiments and observations. His books present us with many indications of a great mind, acute discernment, unwearied application, original remark, bold inquiry, and a clear, forcible, and manly reasoning (k); and every one who considers the surprise which his doctrine occasioned among the anatomists of those days, the strong opposition that it met with from some, and those numerous and powerful prejudices which it had to encounter from the sanction of time and of great names, must allow it was new, and that the author has from its importance a title to rank in the first class of eminent discoverers ancient or modern.
His discovery showed, that in most animals the blood circulates in arteries and veins, and through the medium of one, two, or more hearts: that in arteries it moves from the trunk to the branches; and that, meeting there with the branches of veins, it returns in a languid stream to the heart; that the heart communicates a new impulse; that it drives it on to the trunk of the arteries; and that the arteries, by the thickness of their coats, exerting a force, do push it onwards again into the veins.
In every part of this circulating course, there are valves situated where it is necessary; they are meant to prevent the return of the blood; they are at the beginnings of the great arteries, and are found in different places of the veins where their feeble action requires to be assisted.
The veins, before they enter the heart, generally expand into a thin muscular sac, which is called the auricle. It receives the blood while the heart is contracting; and when the heart admits of dilatation, contracts itself, and throws the blood into the ventricle.
We have here called the ventricle a heart; though what is usually meant by the heart be a ventricle and auricle; or sometimes a ventricle and two auricles, where the veins approach in different directions, and, without bending to meet one another, expand at two different places. Two hearts are sometimes united, so as in appearance to form but one.
From our having mentioned more than one heart, it will be supposed that the modes of circulation are various. In some animals the heart throws its blood to the remotest parts of the system (l); in other animals it throws its blood only into the respiratory organs: from these organs it is collected by the branches of veins; and these branches, uniting in a trunk, convey it to an artery, which renews the impulse, and acts as a heart. In a third set of animals, the blood from the respiratory organs is carried by the veins to another heart; and this second heart, united in the same capillary with the first, distributes the blood by the channel of its arteries to the several parts. In the human fetus, and the fetus of those animals which have two hearts, a part of the blood, without taking the passage through the lungs, proceeds directly from auricle to auricle. In amphibious animals, the auricular passage continues open during their life, and is employed, when the breathing ceases, under the water. In many insects, a number of hearts, or expansions which answer the purpose of hearts, are placed at intervals on the circulating course; and each renews the impulse of the former, where the momentum of the blood fails. In the Sepia Loligo the two separate parts of the gills are each supplied by a heart of its own; the blood from both is collected into one; which, by two arteries opening at two different parts, send it at once to the opposite extremities. In numbers of animals, the heart, like the stomach, is in the extremity opposite to the head.
After the discovery of the circulation, the most interesting object with anatomists was to demonstrate it circulation in a clear, satisfactory, and easy manner. Harvey, to show it with every advantage that he could think of, was obliged to open animals alive: but whether the animals were dead or alive, the larger branches of the veins and arteries were only to be seen, and even these but in certain cases, when they happened occasionally to be full of blood. That admirable method, which is now observed in demonstrating the course of the circulation, we owe to the great anatomists of Holland who flourished in the last century. About 1664, Regnier de Graaf invented the syringe, which is now used, and, accompanied with a print, published an account of it in 1669. His injection was usually a thin fluid of a blue green or some other colour; this injection transfused through the vessels, allowed them to collapse by its general diffusion, and broke out through the first opening that happened in its way. A fluid which hardened after being injected, and which preserved the vessels distended, was a happier contrivance. This at first was either melted tallow or wax, of a colour suiting the taste of the anatomist. So early as the year of Swammerdam, 1667, the celebrated Swammerdam injected the vessels running on the uterus with ceraceous matter; and, jealous
(k) Dr Hunter says, that "none of his writings show him to have been a man of uncommon abilities. It were easy to quote (he says) many passages which bring him nearly to a level with the rest of mankind. He lived almost 30 years after Asellus published the Lacteals, yet to the last seemed most inclined to think that no such vessels existed. Thirty hours at any time should have been sufficient to remove all his doubts; but this subject taken up in self-defence (continues the Doctor) grows unpleasant." Dr Hunter was here thinking of his own discovery when brought in comparison with that of Harvey's. When this comparison was less immediately in view, he says that "Dr Harvey, as appears by his writings, was certainly a first-rate genius for sagacity and application; and his name is deservedly immortal on account of the many observations and improvements he made in anatomy and physiology." Dr Hunter's First Introductory Lecture.
(l) We never exclude the action of the arteries. jealous lest another should claim the merit of such an invention, he transmitted preparations, accompanied with plates, and with a full account of his method, to the Royal Society of London in 1672. Soon after, Of Ruych, his friend Ruych acquired such skill in the art of injecting, that he has not been surpassed by any since his time. He discovered vessels in many parts where they were not supposed to have had an existence; and, contrary to the opinion of the great Malpighi, he showed that even many of the glands were entirely vascular; and that what had been supposed excretory ducts, deriving their origin from some follicle, were but terminations of arteries continued: yet even Ruych could not exhibit in all cases the course of the vessels so well as we do now. Another discovery was yet to be made for demonstrating their small capillary branches running through a part. This was reserved for the very ingenious Dr Nicholle of London; who invented the method of corroding the fleshy parts with a menstruum, and leaving the wax, as it was moulded by the vessels, entire.
From these researches, which evince circulation to be a function so general among animals, some are disposed to think it takes place in all living bodies. But notwithstanding the fashionable language of circulating fluids, of veins, arteries, and even of valves in the vegetable structure; yet nothing performing the office of a heart, and nothing that seems to conduct fluids in a circular course, has been found in plants. In the vegetable kingdom, the chyle is distributed to all the parts from the numerous vessels which convey the sap: and these vessels, being fitted by their structure to carry the sap either downwards or upwards, from the branches to the roots, or from roots to the branches; is the reason why plants inverted in the ground will send forth roots from the place of their branches, and send forth branches from the place of their roots. Even a similar distribution of the chyle takes place in some animals. In the human tenia, in the fasciola hepatica of sheep, and in most polypes, the chyle, without a circulating system, is conveyed directly to the different parts from the alimentary canal. The taste for circulation may at last subside. Till the busyness of absorption from the intestines was, of late, fully secured to the lacteals, we were wont to have also learned dissertations upon a circular motion of the bile. The jaunt which it took was not supposed very cleanly; but it was social: it went with the feces circulation down the intestines, and returned with the blood in of the bile, the mesenteric veins.
Besides the circulation, another circumstance respecting the blood, which sometimes has engaged the concerning thoughts of physiologists, is the colour which it has in most animals. The late Mr Hewson was of opinion, that the lymphatics, with the spleen (m) and the thymus, contributed greatly to the formation of the red globules. He was seemingly led to entertain this opinion from that attention to the lymphatics which made him ascribe much to their power, and from seeing red particles in the absorbents which rise from the splenic and the thymic gland. His reasoning, however, though very ingenious, is not conclusive. The celebrated Nuck, who had often observed a reddish fluid in the lymphatics, assures us, without any hypothesis, that such an appearance was always supernatural; and was either occasioned by a scarcity of lymph, or by some irregular and too much accelerated motion of the blood (n).
It is well known that the blood receives its vermilion colour in passing through the lungs; that animals with lungs have the blood redder than those which are seemingly without that organ; and that the colour, as well as the heat, is in proportion to the extent and perfection of the lungs. It has also been observed, that oxygenous gas is absorbed in respiration; and been proved by experiment, that the red globules of the blood, and the red only, contain iron. It thence would appear, that the colour is owing to iron calcined by the pure air, and reduced to the state of a red oxide. From this manner of conceiving the phenomena, says Chaptal, we may perceive why animal substances are so advantageous in afflicting and facilitating the red dye (o).
A great variety of experiments have shewn how much the colour and consistence of the blood is altered by
(m) Before we can expect to arrive at a proper knowledge of the spleen, we have first to examine its form, its proportion, its situation, its numbers, and its different circumstances in different animals; and as yet this has been done only in a few cases. The gentlemen of the French Academy found, that in the demoiselle it was like the liver, in the bustard like the kidney of a quadruped, in the chamois round and flat, in the lynx narrow and long, in some animals proportionally large, in others proportionally small; that in the gazella it was joined immediately to the stomach, without a vas breve; that in the castor, again, it was attached to the left side of the stomach by eight veins and arteries, and as many vasa brevia; that in the otter, it was fastened to the epipiploon, in the Canada stag to the great ventricle; and they found that in the porcupine and sea-fox it was double. Since their time Dr Monro has observed two large spleens, one attached to the small and the other to the large curvature of the stomach of the squalus squatina or angel-fish, whose blood contains few red particles; and the same eminent physiologist found in a sturgeon no fewer than seven, one of the size of a dried horse-bean, and the rest about the bulk of a dried garden-pea.
(n) Interim non diffiteor vasa illa lymphatica lympham subinde vehere rubieundo colore tinctam, loturae earnis ad instar se habentem. Hoc autem nunguam contingit in statu naturali, verum post nimium et irregularem sanguinis motum. Vel in quivis humidum (ob defectum alimenti) deficit, qua occasione plerique humores vitiantur, et colore preternaturali tingantur. Quid mirum itaque hifce in casibus et lympham reddi sanguineam.
Adenographia, cap. 5.
(o) Chaptal's Chemistry on the Properties of the Blood. The physiologists of last century accounted for the red colour in another way. Rubedo sanguinis (says Verheyen) pro magna parte procedere videtur ab alimentorum particulis salinis ac sulphureis seu oleosis exaltatis. Cujus non leve indicium est, quod lixivium ex cineribus vulgari modo paratum notabiliter rubeat, in quo, praeter aquam, vix aliud quam sal et sulphur, reperibile est:—et lac by the mere action of the vessels; and this discovery has enabled us to conjecture with more certainty than we did formerly, why in infants and phlegmatic persons the blood is paler, in the choleric more yellow, and in the sanguine of vermilion red. It explains likewise, in some measure, why the blood varies in the same individual, not only with regard to the state of health, but likewise at the same instant; and why the blood which circulates through the veins has not the same intensity of colour, nor the same consistence, as that of the arteries; and why the blood which flows through the organs of the breast differs from that which passes languidly through the viscera of the lower belly. This power of the vessels over the blood will bring us also to the true cause why the vessels vary in the density of their coats and in their diameters; why they are sometimes convoluted in a gland; why they sometimes deposit their contents in a follicle; why they are sometimes of a spiral form; why the branches strike off at various angles; why they are variously anastomosed; why they sometimes carry the blood with dispatch and sometimes slowly through a thousand windings. By these means their action is varied, and the blood prepared in numerous ways to answer the ends of nutrition and secretion.
Sect. V. Nutrition.
Nutrition is the function which assimilates the food in the several parts, and which finishes the process already begun in the stomach, in the lungs, and the vascular systems. In perfect animals some of the stages of this process are distinctly marked. The chyle, which has some resemblance to milk, is the work of the alimentary canal: it undergoes some new changes by the action of the lacteals and of their glands, when they exist. In the course of circulation it passes along the respiratory organs, and is mixed with oxygen or some other gas; by this mixture, the consequent heat, and the action of the vessels, it is turned into blood. The blood, when examined, spontaneously separates into three parts; an albuminous part or serum, a coagulable lymph (p), and red globules. The two first are analogous to the white parts of an egg, by which the chick in ovo is nourished; the globules have some resemblance to the yolk, which serves afterwards as food to the chick in the more advanced period of life. The three parts contain each a variety of principles which are originally composed of gases: these principles, conveyed through vessels of various forms, of various diagonals, and with various degrees of motion and of heat, and all along varying as they pass, arrive at last on the confines of the parts Nutrition, which are wrapped up in a cellular tissue or some other membrane. The tissue or membrane gives a new change; the parts nourished perform the office of secreting organs; and as the action of the vessels is varied according to the place to which they are tending and the parts which they enter, we partly see the manner in which bone, muscle, cartilage, and nerve, are all secreted from a common mass.
In worms and polyps, the function of nutrition is assimilated after digestion carried on almost entirely by the cellular tissue; and in plants by a tissue cellular and vesicular cellular. In all living bodies the cellular tissue, besides parts which give a form to the parts, and besides preventing friction and cohesion, certainly performs some important offices. Many have thought it the organ of nutrition; and it surely is one of the organs employed in afflicting to assimilate the nutritious fluid. But it should be remembered, that all the parts of the living body are assimilating organs; that each part assimilates for itself; and that the stomach, the respiratory organs, the vessels, and nerves where they exist, are affilient to the whole and to one another.
It is singular how any should have imagined that the nerves are peculiarly the organs of nutrition, or that concerning growth should be owing to the addition of some organic and vivifying particles pre-existing in the food. These physiologists have not demonstrated the existence of nerves in all living bodies; and these organic and vivifying particles have as yet been discovered but in their fancy. Dr Monro has endeavoured to prove, that the limb of a frog can live and be nourished, and its wounds heal, without any nerves; and Mr Hunter has given many curious instances of a living and nutritious power in the blood.
In plants and animals, the assimilating power has always certain limits prescribed to it: its influence is very generally confined to the sort of food congenial to the species; and its strength is varied according to circumstances; as the age, the habits, and the state of health. Those which are young assimilate faster than those which are old; and one species, which may partly be owing to the nature of their food, will assimilate slower than another. Certain worms that feed on animal and vegetable substances will, in 24 hours in different circumstances, double their former size, but will weigh, according to Redi, from 155 to 210 times more than before. Most oils are of very difficult assimilation; and those which are essential will often resist the long continued and the varied action of the living organs; will mingle easily with diffusely assimilated.
(quod sulphure abundare probat butyri inflammabilitas), si coquatur cum sale lixivioso, colorem plane sanguineum contrahat; quod similliter decoctum ex aqua, sulphure vulgari, et sale tartari ad confectionem lactis sulphuris paratum rubescat; quod cerevisia et quaedam alia diuturniori coctione ruborem contrahentia, illud principium scateant, &c.
Ad intensorem sanguinis rubedinem multum quoque contribuunt particulae nitroae, quae beneficio respirations ex aere in sanguinis massam jugiter transmittuntur: siquidem color ille coccineus magisque splendens quo pallidum sanguis arteriosus a venoso distinguitur, in pulmonibus jugiter altior ac renovatur.
Rubedinem autem hoc modo facile excitari possit amplius confirmatur ex eo, quod vitrum, etiam centum librarum capax per unicum unciam spiritus nutri rafactum, omnino repletum appareat materia rubescente. Verheyen de Sangificatione. Verheyen uses the word sulphur for any inflammable substance.
(p) Senac was the first who discovered this lymph. Secretion. with the parts, and, undecomposed, communicate their flavour.
An assimilating power is not peculiar to living bodies; it is observed in ferments and contagion, and is so obvious with respect to flame which is neither living nor organized, that whole nations who have seen it feeding on inflammable substances, have been disposed to think it was animated, to call it the principle of life itself, and to pay it a kind of religious homage as the proper emblem of that Being by whom the whole universe is upheld.
In living bodies nutrition is only a species of secretion.
Sect. VI. Secretion
Is a function in which a part is separated from the whole, and generally with some change of its qualities. In the case of nutrition it was observed, that all parts secrete for themselves; and that some few, as the lungs, the stomach, the vessels, and the nerves, officiate besides for the general use of the whole system.
If all the ingesta were to remain and to be assimilated, the body would go on continually increasing. But living bodies are constantly in a state of waste and repair. In most animals part of the ingesta is carried off by evacuation, without having entered the mouths of the absorbers; part, which enters the absorbers and veins, is thrown off by exhaling arteries or the urinary passage; and experiments with madder prove that the lymphatics, besides originating from all the cavities and carrying back the lubricating fluids, do enter the substance of the hardest bones, and convey particles that had been assimilated back into the blood.
This office has not been generally ascribed to the absorbers; nor has it been very generally supposed that the blood receives the excrementitious matters of the system, and that one intention of the circulation was either to return them for reaffiliation, or to discharge them by exhaling vessels or by the kidneys. Decayed parts, however, are discovered in the feces evacuated by the intestines, in the clouds, the sediment, and colour of the urine, and by the smell of the perspirable matter. The two last, on certain occasions, and for some time, have often supplied the place of one another; and all the three, the feces, the urine, and perspirable matter, we have reason to believe are remarkably distinguished by two kinds of odour; the one peculiar to the whole species, the other peculiar to the individual. By the perspirable matter which adheres to the ground, and of which the odour is diffused by moisture, the dog not only distinguishes a man from any other animal, but is able to trace his master through a crowd.
The natural evacuations of plants, and of some few animals which feed by absorbers, are all by perspiration or exhaling vessels. The urine in quadrupeds is passed before emission collected in a vesicle, and thence carried exhaling off by the genital organ. In birds, and in a number of fishes, the ureters empty themselves into the rectum, and their contents are evacuated along with the feces.
Besides being used to denote the function, the word secretion is sometimes employed for the matters secreted, fomated, for example, the feces, the urine, and the sweat, and the various useful purpour from the lungs, which are excrementitious, therefor, are secretions which answer useful purposes in the system. Of these the most important and general are the bile, the saliva, the gastric juice, and the pancreatic, which assist in digestion; the lymph and the fat, which lubricate the parts; the mucus, which protects them from acid substances; the nervous fluid, which forms a very conspicuous link between body and mind; the seminal fluid employed in generation to propagate the species; and the lacteal intended for some while to support the young after they emerge from the fetal state.
The saliva is a fluid that mixes with the food in the time of mastication. In man it is secreted from the parotid, the sublingual, and submaxillary glands (q); it is watery and somewhat viscid; it is found to retard and moderate fermentation; it has sometimes a tendency to form calculi like the urine. By these concretions it incrusts the teeth and sometimes obstructs the salivary ducts. It is the seat of the rabies canine.
Upon first examination the gastric liquor seems to possess a solvent power upon animal and vegetable substances without any great preference of affinity. The reason is, it varies according to the nature of the aliment; "it is sometimes acid, sometimes insipid. Brugnatelli has found (says Chaptal) in the gastric juice of carnivorous birds and some others a dilengaged acid, a resin, and an animal substance, united with a small quantity of common salt. The gastric juice of ruminating animals contains ammonia, an extractive animal substance, and common salt. In our time the phosphoric acid has been found dilengaged in the gastric juice of the gramenivorous kinds.
"The bile secreted by the liver is glutinous or im-perfectly fluid like oil, of a very bitter taste, a green colour inclining to yellow, and froths by agitation like the solution of soap. Its constituent principles are water, a spiritus rector, a coagulable lymph, a resinous oil,
(q) These glands are very rarely met with in birds. It is mentioned as a singular circumstance in the demoiselles of Numidia, that "in the lower beak, on both sides of the tongue, under the inward tunicle of the mouth, there were found two glandulous bodies, from whence proceeded several lympheducts which opened into the mouth, and there discharged, being squeezed, a white and viscous humour. There were two of them towards the upper part a great deal bigger than the others. The tongue was flecky at top and cartilaginous underneath, as in hens.
"The tunicle of the palate was rough, with a great number of little nipples and of hard and membranous points. It likewise included a glandulous body, which shot forth two great ductuses opening into the mouth. There was discovered a great quantity of other little glands at the sides of the larynx, which had also some lympheducts." Anat. Descript. of the Demois. of Num. by the French Academy. oil, and soda. The resinous part differs from vegetable resins; because these do not form a soap with fixed alkalis; because they are more acid and inflammable; and because the animal resin melts at the temperature of 40 degrees, and requires a fluidity similar to that of fat. From fat it differs in not being soluble in cold alcohol, in which respect it approaches to spermaceti, which alcohol cannot dissolve without heat.
Bile, like other soaps, removes spots of oil from these substances to which they are adherent; when its passages are obstructed the motion of the intestines becomes languid. It is neither alkaline nor highly putrefactive. In putrefaction it yields something of a musky colour; the fossil alkali precipitates from it a green sediment; and with distilled vinegar it produces a mixture neither acid nor sweet. Like saliva and urine, it has a tendency to form concretions which are called biliary calculi or gall-stones. They are sometimes found of an irregular texture, of a brown, black, yellowish, or greenish colour. They sometimes consist of transparent crystalline laminae, like mica or talc, and are sometimes radiated from the centre to the circumference. They are always inflammable, of a more solid consistence than the generality of animal oils, and resemble spermaceti both in their solidity and crystallization; they are soluble in ardent spirit when assisted by a moderate heat: the warm solution, when filtered, deposits by cooling a number of laminated white brilliant crystals, such as Pouletier de la Salle found in the bile, and which have been compared to the salt of benzoin, the concrete acid of borax, and to spermaceti. Many of their characters indicate that they are a substance of the same nature with the last mentioned. Fourcroy found that the substance of which these crystals are composed exists not only in the crystallized gall-stones or bile; he observed it to a very considerable degree in a human liver which had been exposed to the air for several years, and had lost its volatile parts by putrefaction. He detected it also in a saponaceous form in bodies which had been many years buried under ground; and lately Dr Pearson of London has artificially converted the muscular fibre into a substance of a similar kind, highly inflammable, and resembling spermaceti (r).
The pancreatic juice resembles the saliva, and was examined in the last century, with a good deal of care, by De Graaf and Swammerdam. It has often been observed forming stony concretions (s).
The lymph consists chiefly of water, but, like the serous part of the blood, contains a substance which is coagulable by heat, by acids, and by spirit of wine. It is found in the cellular membrane, in the ventricles of the brain, in the pericardium, on the surface of the pleura, in the abdomen, in the bursa mucöse, and in the joints under the name of synovia, where it has more than an ordinary degree of viscidity and of the lubricating quality. Sometimes, when it stagnates in the sheaths of the tendons and bursa mucöse, it acquires a thickness and forms indolent transparent tumors, which become at last gelatinous. It is secreted chiefly by arteries.
Animal fat is a substance of a nature similar to those oils which are called fat in the vegetable kingdom. Its colour is usually white, sometimes yellow, and its taste infipid. Its consistence is various in different animals. In cetaceous animals and fishes it is nearly fluid: in carnivorous animals more fluid than in the furgivorous: in birds, finer, sweeter, and more unctuous, and generally less solid, than in quadrupeds. In the same animals it is more solid near the kidneys and under the skin than in the vicinity of the moveable viscera. As the animal grows old it becomes yellower and more solid; and in most animals is more copious in winter than in summer. In man and some other animals, it is collected in particular follicles of the cellular membrane, accumulated in great quantities in the groin, in the axilla, in the epiplooon around the kidneys and around the blood-vessels: it is likewise secreted on the surface of the skin which it protects from acid influences, and where it sometimes concretes, often from a want of cleanliness, in the form of small worms. In cetaceous animals and fishes it is generally disposed in certain reservoirs, such as the cavity of the cranium and the vertebrae; in some it is chiefly confined to the liver; in serpents, insects, and worms, to the viscera of the lower belly, where it is disposed in small lumps, and only a small quantity found on the muscles and under the skin: in frogs it is collected in certain bags which diverge, as it were, from a common trunk, and seem like appendages to the ovaria and testes. In many places it seems to be secreted by organic pores, and under the surface of the skin by glands. It is accumulated from a diminution of perspiration, from the nature of the aliment, from morbid affection, and from idiocy. It is of the same nature as the fixed oil of plants; and Lorry has found a striking analogy between it and the bile *.
It is a bad conductor of heat, and preserves the warmth of those regions where it is situated. It is more adhesive and less apt to evaporate than water, and is therefore a better lubricating fluid. When reabsorbed, it counteracts the saline impregnation if too copious;
(r) The means which he uses is digestion in water; and the process supposes a previous acquaintance with what is common and what peculiar to the fibre and the fat. He maintains that the fibre is entirely composed of carbure, oxygene, hydrogene, and azote. In a high temperature these are decomposed, or at least separated, without producing fat. But when the fibre is kept in water in a low temperature, the carbure unites with the hydrogene of the water, and forms a fat resembling spermaceti, and highly inflammable. Part of the oxygene, too, uniting with azote, forms the nitric acid; and part of the azote uniting with the hydrogene constitutes ammonia; so that three substances are thus formed.
(s) De Graaf was of opinion, that calculi might be formed in all glands. He had seen them above twenty times in the pineal gland, that was long thought the residence of the soul:—He says, too, that they occur more frequently in the pineal gland of Frenchmen than of Dutchmen; and very pleasantly affirms this reason, that the volatile spirit of a Frenchman requires more ballast than that of a Hollander. De Succo Pancreatico, cap. 7. It would be impossible here to enumerate or to tell the uses of all the different kinds of secretions in living bodies. We cannot enumerate all that we know without running into tedious detail. The essential oils, camphor, the gums, the balsams, the resins, and other secretions, many others, are various secretions of the vegetable kingdom. Each species of plant and animal has generally some peculiar secretion; and this secretion in the individual has often some distinguishing quality, discoverable by taste, by colour, or by smell. These different secretions have likewise each their particular uses. We know the intention of the oily juice with which the bird dresses its feathers, of the glutinous fluid of the fish, of the viscid mucilage of the snail; we see the purpose for which the viper sometimes employs its virulent humour, and for which the scuttle-fish ejects its ink; but yet we know only in part.
The difference among the various secretions of the same system seem principally owing to a difference of stimulants, and to some difference in the action, the form and the irritable power of the secretory organ. Passions of the mind very often affect the secretions; and it frequently happens that passion and medicine affect one secretory organ and not another. It is therefore probable that the organs of secretion, and the smallest fibre is an organ of this kind: we say, it is probable that the organs of secretion, like the eye, the ear, and all the different organs of sense, are each affected in some measure by peculiar stimulants; as the stomach by hunger, the fauces by thirst, and the genital organs by venereal orgasms.
Fermentative mixture, and some original impregnation of the organs, have also been brought to explain the several phenomena of secretion. We conclude with observing, that however much the various fluids of living bodies may differ in appearance, chemical analysis has generally reduced them to water, a gluten, a saline impregnation, and an oil.
Sect. VII. Integumentum.
All living bodies are furnished with one, two, or integuments with more integuments, which are prepared by secretory organs, and which are a defence against those injuries to which their situation is commonly exposed. Of these integuments, some prevent the diffusion of the fluids, some again resist acid and corrosive substances, some are indigestible in the stomach, indigestible in the bowels, and some are seemingly incorruptible in the earth. By these properties they preserve seeds and the ova of insects for a number of years, waiting the change of eruption in soil or of season. They protect both from the action of the earth, of weak membranous stomachs, and make those animals who choose to swallow them contribute likewise to their propagation. The gelatinous substance ejected by birds, and called the tremella-nigra or starfish, we have lately found, by numerous experiments, to be a substance of this kind. It is nothing else than the oviducts of frogs, which, as the embryo in form of an egg moves along their winding canal, are intended by nature to secrete that transparent and viscid glaire which
(1) The efficient cause may be diminished by perspiration. which constitutes the albuminous part of the ovum, and feeds and protects the embryo in water (v).
Some integuments are chiefly useful by their strength and hardness. The shells of the beetle are an excellent defence for the membranous wings which the creature is seen to pack up in folds when it inclines to creep into the earth. The shell of the snail lodges the intestines (x) when the animal comes forth to seek for its food, and it furnishes a safe retreat for the body when any danger is threatened from without. Some animals, confined to their shells, can open and close them by a muscular power; and some shells, like the scales observed on fishes and insects, are disposed into plates, so as to be no hindrance to motion. Several insects which spend a part of their time in the water always compose a shell for themselves where it is needful. The usual materials are sand, straws, or mud, which they cement by a viscid secretion. The shells of most insects are corneous. Swammerdam found that cretaceous shells are composed of layers of indurated membranes, and that they are sometimes covered with a cuticle.
Some integuments are covered with feathers, some with hair or a thick down. Besides many other obvious uses of these coverings, they serve in general to repel insects; and being bad conductors of heat, maintain a genial and necessary warmth.
When the integuments are covered with prickles, they repel attacks by the strength of their points, or by the venom which they infuse, as the stings of nettles and the downs of some insects and plants.
When they are moistened with a viscid secretion, they preserve the necessary softness of the parts, prevent evaporation, resist acrimony, enable plants to destroy their enemies, and assist the snail in performing its motions.
Both plants and animals, but particularly the former, are often protected by an odoriferous effluvia from their integuments. This effluvia is the finer part of their volatile oil, always inflammable, and so subtle, that the continual emission of it from wood or flowers does not sensibly diminish their weight. To this fragrance it is owing, that the deadly nightshade, the henbane, hounds-tongue, and many others, are seen on almost every high road untouched by animals. The muscimole-tree of the West Indies emits so very dangerous vapours, that the natives poison their arrows with its juices, and those have died who have ventured to sleep under its shade. The lobelia longiflora of America produces a suffocating oppression in the breast of those who respire in its vicinity. The return of a periodical disorder has been attributed to the exhalation of the rhus toxicodendron. Every one knows, says Chaptal, the effects of musk and oriental saffron on certain persons. Ingenhouz mentions a young lady whose death was occasioned by the smell of lilies; and Triller reports an instance of another who died in consequence of the smell of violets. The selection of grasses by different animals seems to be owing to the manner in which the volatile aroma affects their senses. But of all the vegetable exhalations known, those emitted by the bohun-upas, or poison-tree of Java, are the most remarkable. For many miles round no animal can breathe the air, no plant dares to peep from the foil, the fishes die in the poisoned stream, and the birds that venture athwart the atmosphere with despairing shrieks sink down lifeless. Such often is the use of the fragrant oils in the vegetable economy. The shrubs and trees that are covered with thorns are in general a grateful food to animals. They generously avow their manner of attack, and scorn the dark assassination by poisons.
The various colours of the integuments, as well as by their aroma, is a species of defence. "Caterpillars which colour feed on leaves (says Darwin) are generally green; and earth-worms the colour of the earth which they inhabit. Butterflies which frequent flowers are coloured like them. Small birds which frequent hedges have greenish backs like the leaves, and light-coloured bellies like the sky, and are hence less visible to the hawk who passes under them or over them. Those birds which are much amongst flowers, as the goldfinch, are furnished with vivid colours. The lark, partridge, hare, are the colour of dry vegetables or earth on which they rest; and frogs vary their colour with the mud of the streams which they frequent (y), and those which live on trees are green. Fish which are generally suspended in the water, and swallows which are generally suspended in the air, have their backs the colour of the distant ground, and their bellies of the sky." The sphinx-convolvuli, or unicorn-moth, resembles in colour the flower on which it rests; and among plants, the nectary and petals of the cphrys, and of some kinds of the delphinium, resemble both in form and colour the insects which plunder them, and thus sometimes escape from their enemies by having the appearance of being pre-occupied. From colour being thus employed as a defence, many animals vary their change of colours with the seasons and circumstances; and those colour which are of different colours in summer according to the places which they inhabit, do all in winter assume in common the colour of the snow.
But a change of colour is not the only change of the integuments. As the outmost are often insensible to stimulants, and for obvious reasons possess little of the vital principle, in all cases where they cannot be enlarged to admit an additional increase of growth, or where they are not furnished with necessary organs to repair those injuries which they may suffer from disease or accident, the body is endowed by nature with a power to throw them off, and to produce others in their stead (z). For this reason we see the tree casting annually its exterior bark, the lobster his shell, the bird
(v) We have often inflated the oviducts of frogs, and dried them; and afterwards putting small pieces of them into water, have seen them swollen in a few hours to a large size, and forming the tremella-nostoc or starfall.
(x) This snail is found in our gardens, and carries its shell, including the intestines, upon its back.
(y) The same is the case with many fishes that live in lakes.
(z) Several small animals in changing their integuments change likewise the interior coat of the alimentary canal, which they void with the faeces. Irritability, bird his feathers, the quadruped his hair, and sometimes his horns, the serpent his skin, and man himself renewing the scales of the epidermis. These changes usually take place once a year, twice frequently with respect to serpents, and oftener in toads, who have been observed to devour the skin which they throw off. All the integuments of owls and snakes, being wholly the production of parental organs, neither are nor can be repaired.
Sect. VIII. Irritability,
Is that property of the living fibre by which it acts in consequence of stimulants. Being one of the great causes of motion in living bodies, no property has excited more wonder, been the cause of more error, or exhibits such a number of striking phenomena to the senses. These effects, however, have arisen rather from the nature of the stimulants than from anything mysterious in irritability. Many of the stimulants by which this property in bodies is displayed are often invisible, unknown, or unthought of; and men being conscious that a number of their motions proceed from some strange or stimulant, that is, under the direction of a mental power, they readily conclude from a sort of analogy, that every motion in plant and insect that seems to answer a useful purpose, and is caused by some invisible stimulant, is the consequence of mind directing from within. They further suppose that irritability is in all cases the consequence of nerves, which are those organs which nature has employed in the animal kingdom to convey stimuli between body and mind. These singular conclusions have led to others that are less admissible even than themselves. It has been imagined that creatures the most stupid possess within them a principle of mind that is incapable of further improvement, but which notwithstanding is in many respects superior to reason, and a surer guide in whatever relates to self-preservation or that of the species: it enables the animal to predict without foresight, and to act rationally without intelligence. This wondrous principle has been called instinct; and in order to account for some of the singular phenomena of vegetables, a share of it has graciously been allowed to plants; irritability, which having become favourites of late, have been also presented with the privilege of sensation, permitted to fall in love, and to marry, and on some occasions to exercise the faculty of volition.
At these conceptions the metaphysician will naturally smile. He knows how many impose on themselves by the mere sound of their own words, as if by calling the snow black they were to discover a new property; which curious discovery would turn out at last to be only a gross ignorance of language, and the foolish misapplication of a syllable. He who has studied the philosophy of mind, and been accustomed to view objects through another medium than the magic colourings of passion and of fancy, readily perceives something of absurdity in ascribing such wisdom to plants and insects. With respect to animals, these gentlemen do not recollect that voluntary actions are of two kinds, as they proceed from design or propensity; that in performing one of these kinds the mind itself has an object in view, and is properly the source whence they from design originate; but that in the other the mind is merely a secondary agent, is acting under the influence of its fixity. Irritability, is often not aware of the consequences, or although aware is often so infatuated as not to regard them, however fatal. It is generally well known to the naturalist, that not a few of these propensities arise from the form and structure of the body, from the manner in which the optic nerve is affected by air, colours, the olfactory by smells, the gustatory by tastes, and the auditory by sounds; from the different ways in which the senses are affected by thirst, the stomach by hunger, and the genital parts by venereal orgies.
Besides these and other propensities which operate as stimulants in the system itself, the naturalist has found that light, heat, and moisture, in various degrees, from absolute darkness, coldness, and dryness, of nerves, act as stimulants upon living bodies: he has experienced that electricity is a general agent, that several plants emit flashes (a), and that some animals even give shocks resembling the electric. He has made it probable that
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(a) "In Sweden (says the author of the Loves of the Plants) a very curious phenomenon has been observed on certain flowers by M. Haggereen, lecturer on natural philosophy. One evening he perceived a faint flash of light dart from a marigold: surprised at such an uncommon appearance, he resolved to examine it with attention; and to be assured that it was no deception of the eye, he placed a man near him with orders to make a signal at the moment when he observed the light. They both saw it constantly at the same moment; the light was most brilliant on marigolds of an orange or flame colour, but scarcely visible on pale ones; the flash was frequently seen on the same flower two or three times in quick succession, but more commonly at intervals of several minutes; and when several flowers in the same place emitted their light together, it could be observed at a considerable distance. This phenomenon was remarked in the months of July and August at sunset, and for half an hour after when the atmosphere was clear, but after a rainy day or when the atmosphere was loaded with vapours nothing of it was seen. The following flowers emitted flashes more or less vivid in this order: The marigold, garden nasturtium, orange lily, African marigold; sometimes it was also observed on the sun-flowers; but bright, yellow, or flame colour, seemed in general necessary for the production of this light, for it was never seen on the flowers of any other colour. The flowers were carefully examined with a microscope without any insects or phosphoric worms being found. M. Haggereen, after having observed the flash from the orange-lily, the anthers of which are a considerable space distant from the petals, found that the light proceeded from the petals only; whence he concludes, that this electric light is caused by the pollen which, in flying off, is scattered upon the petals (Observ. Physique par M. Rozier, vol. xxxiii. p. 117.)"—Addition to the note on Tropoleum, the Loves of the Plants. The author of this beautiful poem supposes, that the time of the twilight is sometimes extended by different bodies emitting the light which they had absorbed during the day." Irritability, it produces all the wonders of crystallization; and that the cause of chemical affinity, and of all the phenomena displayed by the magnet, if not simply a modification, is at least akin to it. In the male parts of plant and animal, he has seen both the fluid and the pollen that give the stimulus in generation, and are accompanied with so extraordinary changes in the system. He has found that much of the vegetable economy, and that even the function of generation itself, as the development of the fecundating powder, and its application to the female organ, is partly carried on by wind, heat, and other such agents. He has reason to conjecture that many general agents in nature are yet unknown. By the help of chemistry, he has found out lately a considerate number which are called gases, which are of the very highest importance in both the animal and vegetable economy, and which, like the aromas of plants, or the causes of contagion, produce their effects without being visible. It is only, too, of a late date that the celebrated professor Galvani of Bologna has excited so much curiosity through Europe, by the discovery of a certain stimulus that resides in the nerves, that passes along electric conductors, and which by a certain application of metals occasions a vivid flash in the eye, convulses the body of a living frog, and rouses the detached limbs into action. The change of colour in the integuments according to different seasons and circumstances, though it answer a rational and useful purpose, proceeds from a cause that does not seem to be very well known. Even many agents which are not invisible, nor yet unknown, exert their influence in a secret manner, so as not to be obvious to the senses. It is generally known that many singular movements of plants are owing to heat, many to light, and several to moisture. The barley-corn is often observed to creep on the ground by means of its awn, which dilates and contracts according to the different degrees of moisture. The wild oat, employed as an hygrometer, moves through the barn, travels through the fields, nor ceases to be changing its situation till its beard fall off, or till it meet with a soil where it conveniently may strike root. Upon a similar principle of motion, the ingenious Edgeworth constructed an automaton which moved through a room which it inhabited. It is easily conceived how these singular effects, arising from causes that are unknown, invisible, or unthought of, should give birth to the notions of witchcraft and of instinct, and impress the fancy with an idea of something resembling sensation and volition in the vegetable kingdom. These agents, whether invisible, unknown, or unthought of, directed by regular and uniform laws under the great Author of nature, produce effects that indicate prescience, wisdom, and design, and causing a transient or permanent propensity in the mental part, frequently control resistless sway the finite minds that reside in matter. These minds, in a living body, have generally been found accompanied with some system of nerves; and these nerves happening with equal facility and promptness to convey stimuli from the mind to the body and the body to the mind, the great difficulty has been to determine with respect to others when the action proceeds solely from design, solely from propensity, or from design and propensity together. The uniform conduct of the brute creation would seem to imply that their minds have little of inventive power; that it generally acts from chiefly from the impulse of propensity; and that its manners are varied, not in consequence of a change of sentiments, but from the induction of new habits, and the application of new stimulants.
It has been observed, that in all animals the vigour of mind has some relation to the quantity of brain, and vigour of to the perfection of its organization; and that the mind acuteness of the different senses is generally proportioned on to the quantity of nerve bestowed on their organs (b). The brain of Man has a greater proportion of brain than any other animal; but many an animal has a much greater proportion of nerve bestowed on different organs of sense. Many animals have therefore acuter senses than man; but man has a greater vigour of mind than any other animal on this globe.
The brain of quadrupeds is somewhat similar to that of man, but proportionally smaller, and not perhaps so well organized. Willis has observed, that among quadrupeds the structure of the cerebrum is more variable than that of the cerebellum; that the former generally furnishes nerves to the voluntary muscles, and the latter with the medulla oblongata to the involuntary. He has likewise remarked, that the round prominences commonly called the nates and testes are large in the quadrupeds, which are active and vigorous, and in some measure able to procure their own subsistence at birth; that the tuber annulare is large in the quadrupeds that are distinguished for their sagacity; that wherever the tuber annulare is small, the prominences are large, and wherever it is large the prominences are small. From these observations he has concluded that the tuber annulare is the seat of genius, and the round prominences the seat of what has been called instinct (c).
The brain of birds is seemingly the reverse of the human brain; the cortical substance is the interior, and the ventricles are situated in the white part on the outside. In the brain of the bird there are no circumvolutions like the intestines, no fornix, corpus callosum, nor corpora striata.
The brain of fishes is in many respects similar in its structure to the brain of birds. It is very small in proportion to their body, and is generally surrounded with an oily matter. In one genus of fishes, the garrus, Dr Monro found spheroidal bodies between the dura-
(b) The acuteness of the senses depends upon the readiness with which their organs are affected by stimuli. This readiness depends on irritability. It is not necessarily connected with mind, nor should it ever be confounded with perception, which in classical language signifies a property of the mental principle.
(c) Few perhaps who have dissected different animals, and who, besides a number of structures, have seen a variety of tubercles and lobes existing in the brain, will be rash in ascribing to any one of them one particular office. The pineal gland was for some time thought the seat of the soul. It was afterwards found to be of ten
Irritability dura and pia mater, and covering the greater part of the nerves like a coat of mail. The two fenuses, seeing and hearing, in many fishes are often acute. By laying one ear on the water, and striking the surface at some distance, this element is found to be a better conductor of sound than even the air.
The reptile tribes have very little brain, and like the fishes have no ganglia upon their nerves.
Most insects have no brain at all, but a nervous cord that is full of ganglia, that runs from one extremity to the other, and is denominated the spinal marrow. This knotty cord, however, is not marrow; the insect has nothing resembling a spine; and the situation of the cord in the animal is often not along the back but the breast. In the silk-worm, and most other insects, this cord is in contact with the alimentary canal; and the first ganglion, which is sometimes called the brain, though not in the head, divides, in order to give a passage to the stomach, and again unites in a second ganglion. Swammerdam found in a species of snail a brain with two lobes, in contact with the stomach, moveable by muscles, and without a fixed place in the body.
The polypes exhibit no appearance of brain or of nerve, as in other animals. Their skin, however, is observed to be full of a number of small granular bodies, which are connected by a glairy matter that resembles a thread. Like rows of bead-strings, they extend from one extremity to the other, and along the arms. Trembley learned from a number of experiments that they received their colour from the food, and therefore supposed them to be vehicles or glands. If not like the tuberous nerves of the insects, they at least are not very different in appearance from the nerves of the gadus that are covered with a number of spheroidal bodies like a coat of mail.
Some things would insinuate that a nervous system does not seem to be necessarily connected with mind under other causes besides mind. Even many nerves are not subjected to the influence of mind; and the mind often by its own inattention may lose the power which it originally possessed over nerves. Many persons can move the muscles of the ear, and others may have lost that power through neglect. After Fontana had observed that the heart was a voluntary muscle in a wheel polype, he learned to retard and accelerate the motions of his own at pleasure. If some nerves, from a sort of prescription, thus cease to be obedient to the power of mind, others by frequent service and habit become so obedient as to convey their stimuli to the muscles almost without the consciousness of mind. The motions excited by the stimuli of nerves are in many cases exceedingly rapid. These may be seen in the wings of most insects, but are most noticed in dancers, tumblers, and apes, and all those animals that are exhibited for feats of agility.
The motions which we see excited in the body by the great stimuli of nerves have often been so vigorous and prompt, as to have torn the muscle from the bone, and the nerves to have broken the bone itself. They often affect the organs of secretion, have often unhinged the fabric of the system, occasioned death, and accounted for the miracles that have been ascribed to the power of fancy. The prompt motions of what have been named sensitive plants seem owing to a different species of stimulants acting on extremely irritable fibres.
In the animal kingdom all muscles in the time of action
ten filled with stony concretions; and the celebrated Nuck, instead of assigning to it any prerogative, contented himself with writing its epitaph.
VIATOR Gradum. Silet. Omni Conatus. CONARIUM. Respicie. Sepultum. Partem. Tui. Corporis. Primam. Ut. Olim. Volebant. Anima. Sedem. GLANDULAM. PINEALEM. Hoc. Seculo. Natam. Et. Extinctam. Cujus. Majestatem. Splendoremque. Fama. Firmaret. Opinio. Conservat. Tamdiu. Vixit. Donee. Divinae. Particulae. Aura. Avolaverat. Tota. LYMPHAQUE. Limpida. Locum. Suppleret. Abi Sine. GLANDE. Viator. Lymphamque. Ut. Aliis. CONARIO. Concede. Ne tuam Posteri Mireatur Ignorantiam.
(b) In many instances the prompt motions of animals seem more owing to the irritability of their fibres than to what has been called the sensibility of their nerves. The poet was mistaken when he supposed that the mangled insect would feel as sensibly as a mangled giant. When the gad-fly fixes fairly on the hand, you may cut off its wings, its legs, its antennae, and a part of the lower division of its body, without disturbing its gratification, or apparently occasioning to it much trouble.
Irritability; action are observed to discharge a quantity of their blood; and those muscles which are naturally white are what most irritable. In all living bodies, the irritable fibres are power will cease to obey the action of a stimulant if most irrita—either long or violently applied. After exercise, therefore, the irritable fibre requires rest, after heat cold, when long continued. This is the reason that in plants and animals there are certain exertions and functions of the system that can only be continued at intervals and seasons. The natural stimuli of involuntary muscles continue to act, and the muscles continue to obey through life.
The organs of sense were formed to mark the difference of stimulants; yet living bodies are affected by light without having eyes, by sounds without having ears, by odorous effluvia without having smell, and by rapid bodies without having taste. It is easily conceived how these objects, by their inherent properties or motion, may produce a confused sort of excitement in every highly irritable fibre. But the organs of sense are peculiarly fitted to receive accurate and distinct impressions from each of these objects; and these different impressions seem not to arise from any difference in the kind of nerves by which they are received. All the difference that has been observed arises from the structure of the organ itself, and from the manner in which the nerve is distributed through it. Other parts of the animal body, as the stomach, the fauces, and genital organs, are thus affected by particular stimulants; and many animals, and even vegetables, may be affected in various manners, and by various stimulants, of which neither our feelings nor our senses can give intimation of anything analogous.
With respect to the several organs of sense, some animals have many eyes without any motion, and some animals have few eyes with varieties of motion. The entrance to the ear in some animals is from the mouth, as happens in the frog; and the bones of the ear are without the cranium, as in some fishes. The sense of smelling is found in the nose: this sense is astonishing in dogs; and even sheep, in distinguishing their lambs, trust to it more than to seeing or hearing. The sense of taste is far from being general; and the sense of touch can hardly be said to reside peculiarly in any one organ.
Sect. IX. Motion.
IRRITABILITY is one of the great sources of motion in all living bodies; and this power is brought into action immediately by nerves or some other stimulants. Locomotion here is principally considered; for although the kinds of internal motion employed in secretion and the other functions be as remarkable, in the eye of the philosopher they have not so generally attracted the attention. Most animals are capable by nature of changing the place which their body occupies; for this reason the irritable fibres being formed into bundles, which are called muscles, are in most animals attached to bones, cartilages, or hard integuments, which they move as levers: these levers, with their muscles attached, are in most cases formed into wings, fins, and legs of various kinds, and are employed in performing the motions of flying, swimming, walking, leaping, and creeping. So very necessary, in the opinion of some of the ancients, was one or other of these instruments performed to progressive motion, that the movement of the ferry, fins, pent was often ascribed to a supernatural cause, was supposed to resemble the incipit deorum, and procured to the animal one of the highest and most honourable ranks among the emblematic kinds of divinities. Even Moses himself, who was unwilling to allow it the character of an agathodemon or good genius, was yet so much puzzled at its being able to move without feet, that he pronounces it a tool of the devil; and says that it was deprived of its feet by a curse from heaven for seducing mankind into idolatry. Notwithstanding, however, the surprise that has been occasioned by its singular movement, the motion of snails, though not so rapid, is in many respects as extraordinary: they adhere by a certain viscid secretion, on dry ground this secretion forms a pavement over which they glide; and they proceed by the action of muscles without bone, cartilage, or shell, to which these muscles can be attached.
No animal walks without legs or flies without wings (§); but there are many that swim without fins, and that leap and creep without any legs. The rapidity of movement is not proportioned to the number of instruments that are employed: if the spongy fish be observed to move slowly with one leg, the sea urchin moves still slower with many thousands; the oyster moves by squirting out water; the scallop by the jerk of its shell, and when in the water it rises to the surface and sails before the wind.
Many animals are formed by nature to fly, walk, leap, and swim: the fate of those is rather uncommon of locomotion, whose muscles or feet are by nature attached to their integuments; the lobster is obliged to throw off its shell, and the caterpillar all its feet with the skin, and in that situation to remain stationary till it receive new instruments of motion.
Whoever has read the celebrated work De Motu Animalium, needs not to be told that, besides the organs which are here mentioned, the form, the structure, and even the specific gravity of the body, as determined by air, vehicles, and bubbles, with a great variety of other circumstances, are necessary to explain the different phenomena of locomotion.
As to vegetable motions, they evidently depend on motions of external agents: The motion of the wild oat has been vegetables mentioned; the wings of seeds only fit them to be carried by the wind, their specific gravity to float in the water, and their legs or tentacula to adhere to bodies that are in motion; the singular motions which have been ascribed to sleeping, to waking, to sensation, and volition, in the vegetable kingdom, seem only the consequence of light, heat, moisture, and such stimulants, acting invisibly or with secret influence; the opening and closing of the meteoric flowers are always correspondent to the states of the atmosphere; and the opening and closing of the equinoctial and tropic flowers, to the light, the length, or shortness of the day.
(§) The fins of the flying fish enable it rather to spring than fly. The principal intentions of locomotion are to get foo; to shun danger, to promote intercourse, and diffuse the species.
Sect. X. Habit.
Habit here deviates a little from its usual meaning. We employ it to signify that principle in living bodies by which they accommodate themselves to circumstances, assume as it were a different nature, and in many respects undergo a species of transformation.
So very much do some individuals of the vegetable tribe accommodate themselves to different situations, to soil, to climate, and the state of cultivation, that those naturalists who have not been accustomed to nice and accurate discriminations, have frequently mistaken the variations of the same plant for so many species. These variations may be daily seen by examining the plant as it grows on the mountains, in the valleys, in the garden, or in the fields; or by bringing it from a rude uncultivated state, when it sometimes lays aside its formidable prickles, and changes the colour and structure of its flowers.
In the plant and animal, the delicacy and vigour of the constitution are often the effects of habit and circumstance than original conformation. We have mentioned already the varying colour of the integuments, and the purpose which it serves in changing with the seasons. We may here add, that animals covered with a down or hair have it thick or thin, long or short, according to the different exigencies of climate.
Those changes produced on their body are accompanied with others which are the causes of new tastes, of new propensities, and new manners. At the Cape of Good Hope the ostrich inclines to sit on her eggs day and night like any other bird; but in Senegal, where the heat is great, she is somehow disposed to leave them to the sun during the day. In those countries where provisions can be found during the greatest part of the year, the bee gradually loses the propensity of laying up stores for the season of winter; and in those countries infested with monkeys, many birds (says an amusing and instructive writer) which in other climates build in bushes and the clefts of trees, suspend their nests upon slender twigs, and by this ingenious device elude the capacity of their enemies.
Man, from imitation, is exposed to a great number of habits peculiar to himself; and physical causes have ingeniously been assigned for the variety of his features and complexion.
Few experiments have yet been instituted with a view to show how far this accommodating principle in nature may be extended in the different species of plants and animals. It is known, however, that the lamb and the dove can be made carnivorous; and that the hawk, laying aside his ferocity, can be brought by art to live upon grain.
Of all the effects of this singular principle, the most wonderful are those which are seen to take place with respect to generation. The fact is far from being new to the naturalists, that certain animals, oviparous at one season, are viviparous at another. This indicated much of accommodating power, though far inferior to what has been since witnessed and displayed: for who from all this could suspect, that any animal which usually propagates by an intercourse of sexes, could in any circumstance accommodate so far as to multiply its species another way. Bonnet of Geneva, however, has discovered, that the puceron or vine fritter, which generally propagates by an intercourse of sexes, is not only oviparous at one period and viviparous at another, but in all cases where the union of the sexes is not to be obtained, can easily accomplish all the purposes of generation without it. Similar experiments have likewise proved, that many plants can bring to maturity a productive seed, though the male parts of the flower be destroyed before they can in the usual way have any impregnating effect on the female. In this case the conclusions drawn have been somewhat new. From these experiments it has been inferred, that the sexual system is ill-founded, and that most of the learned naturalists of Europe are on this subject labouring at present under a mistake. This reasoning, however, is not satisfactory: for why, it might be asked, in the vegetable kingdom more than in the animal, should the mode of generation be necessarily uniform? Those plants may, like some animals, propagate without sexual distinctions, the conclusion is not logical that these distinctions are useless in all; and though some few may, in particular instances, propagate without that impregnation to which they were accustomed, will any one demonstrate, that accommodating nature does not here as in the puceron adopt a new method to accomplish her designs?
In all living bodies, it frequently happens that several characteristic distinctions, as the colour, the fastidious and tares, and a number of diseases that are originally the effects of circumstance, do at last become fixed in the system, that they are afterwards transmitted to posterity through some generations (p.). With regard to animals these facts are well known; and as to vegetables, it has been observed by a pupil of Linnæus, that the apple-trees which are sent from Britain to New England blossom at first too early for the climate, and
(1) Might not these facts reasonably claim the attention of those who mean to form matrimonial connections? How many might easily entail on their posterity hale constitutions, regular features, beautiful forms, sound minds, and tempers at once uniform and cheerful, who yet, from their fond desire of wealth or their fond admiration of high rank, bequeath to them only scrofulous habits, deformed persons, disagreeable features, mean understandings, and forbidding tempers. Excepting the more extraordinary properties of body and mind, there are few that may not in some measure be transmitted to posterity: but nature seems unwilling that what is very eminent should ever be extended to a genus or a species; and therefore the sons of Cicero and Cromwell are only two of a thousand instances that might serve to prove, that neither extensive nor eccentric geniuses can be made hereditary: in the second generation they often degenerate into minds that are weak, fatuous, or deranged; or into minds that are chiefly remarkable by their oddities and whims. and bear no fruit; and that it is only after some years that they conform to their situation; and this circumstance, by the way, explains why roots and seeds germinate sooner when brought from southern than when they are brought from northern latitudes. The very permanency of these effects has often been the cause of much confusion and error in philosophy: for the naturalist, mistaking the lasting though temporary qualities of habit for the real and essential qualities of species, has not unfrequently drawn conclusions from his experiments that have been contradicted by similar experiments in other circumstances. This is one of the obvious reasons why experiments exhibit so many incongruencies and contradictions; and why we are amused with such a multitude of visionary theories about the properties of living bodies.
From not attending to the numerous circumstances that induce habits, and to that general accommodating principle in living bodies, many medical prescriptions are found to be not only useless but mischievous; and many parents, by studying the health and comfort of their children, bring on habits that prove the sources of perpetual sickness or the certain presages of an early death.
The accommodating principle is one of the consequences of irritability. Its various effects arise from the actions of different stimulants on the irritable fibre; and the after-duration of these effects, from the modifications of the irritable fibre, become habitual from the frequently repeated action of the stimulants.
The design of this accommodating principle is to fit both the plant and the animal for a more extensive and a more varied range of existence.
**Sect. XI. Transformation.**
More remarkably striking than any of those changes to which the plant and animal are exposed, from the variations of habit or the change of integuments, are those alterations which they undergo from metamorphosis or transformation. It has indeed been asserted, that these alterations consist in throwing off certain temporary coverings or envelopes; but there is here a want of precision in the ideas, and consequently a want of accuracy in the expression. The same persons who make this assertion inform us, that caterpillars change their skin, and many of them even several times, previous to the period of their transformation. Transformation, therefore, and a change of integuments, by their own conceptions, are different things. The truth is, transformation frequently takes place independent of any change of integments; and there is often a change of the integments without transformation or any appearance of a new form: but a new form or change of appearance is always implied in metamorphosis or transformation. This new form is sometimes occasioned by a change of shape, consistency, and colour; as when the lobes of a seed are converted into seminal leaves. It is sometimes occasioned by a change of proportions among the parts: the proportions of a fetus, every one sees, are different from those of a full grown man; and the painter, merely by observing the proportions, represents a child, a dwarf, and a giant, on the same scale. It is sometimes occasioned by the addition of new organs; as when the emmet receives wings, and the plume of the seed is fed by new roots striking into the ground; or it is occasioned by a change of both the form and the organs, and their mode of operation, as happens remarkably in some insects; for though all living bodies, plants and animals without exception, undergo partial or general transformations, yet these changes are chiefly observable among insects. Many insects appear to consist of two distinct animal bodies one within the other: the exterior, a creature of an ugly form, residing in the water or under the earth, breathing by gills or sometimes by tracheae projecting from the tail, possessing a voracious and groveling appetite, and having a system of sanguiferous vessels that circulates the blood towards the head. When all its parts decay and fall off, the creature inclosed succeeds in its stead: this often is an animal of a different form, generally lives in a different element, feeds on a different species of food, has different instruments of motion, different organs of sense, different organs of respiration, and differently situated; and being endowed with the parts of generation, inclines to gratify the sexual propensity, and produces an embryo which becomes like the first, and from which afterwards in process of time a creature is evolved similar to itself.
If the embryo or egg be deposited on a leaf, the accommodation frequently is observed to bend, to wrap it in folds, dating principles intended for the purpose, and to protect it from injuries and danger. If deposited in the body of an animal or plant, they accommodate themselves to its wants and necessities, and furnish a tumour which serves it for a nidus, and besides, like an uterus, supplies it with nourishment; and if deposited in the body of an insect, the creature provides for the future generation of its young charge with all the tender care of a parent, and then dies.
These circumstances, added to the great variety of Difficult forms which insects assume, render it sometimes difficult to know who is the parent. We cannot, for instance, pronounce with certainty who is the true parent of the gordius, known by the name of the *seta equina*, or hair eel. A set of experiments, which we once began with a view to throw some light on the subject, were interrupted unfortunately by an accident, and we have not since had leisure to resume them. We learned only, from a number of observations, that certain black beetles about the end of the summer months have the strongest propensity to run into the water, where they soon die; and that one or two, and sometimes three or more, of those eels gradually drop from the beetle by the anus. Whether other insects provide for the gordius in this manner we have not yet been able to determine.
The transmutations of some animals are most observable in the uterus and egg. Some early transformations of the chick may be seen in the plate belonging to this article; and anatomy has often witnessed the change which happens at birth with respect to circulation, respiration, digestion, and the other functions.
If the reader wish to be much acquainted with the manners and transformations of insects, he will derive information and pleasure from consulting the plates and memoirs of Reaumur. If he wish to know their intimate structure, the laborious Swammerdam can introduce him to a new and amusing species of anatomy. This last author had before Reaumur defined and described Physiology.
Transformed the kinds of transmutations among insects and some other animals. He has shown similar transmutations in plants; and in plate 46 of his Book of Nature, has compared the frog and the clove July-flower under their six different forms.
In all living bodies possessed of mind, the changes of form, as well as the change of habit and of age, are usually accompanied with new propensities, appetites, and passions. It may therefore be inferred, that we ought not to look for the cause of temper in either the brain or the nervous system; or to imagine, that the propensities, appetites, and passions, are properties of mind: they seem only affections happening to mind in consequence of stimuli and organic structure.
Microscopic observations having demonstrated, that all the forms of the plant and animal existed previously in the seed or embryo, transformation must be owing entirely to the evolution of the different parts by means of nutrition.
What nature intends by transformation, we pretend not to say; but by means of transformation different elements are peopled, the different scenes variously adorned, and animated nature wonderfully diversified without a multiplication of beings.
Sect. XII. Generation.
Many of the causes which contribute to the formation of a living body have hitherto eluded human research; may in all probability never be discovered; and perhaps are beyond human comprehension. Some philosophers, considering the extreme divisibility of matter, and learning from the microscope that transformation is but the development of certain parts that previously existed, have thence imagined that generation is somewhat analogous; that all regularly organized bodies received their form at the beginning; that the first of every genus and species contained by involution the numerous millions of succeeding generations; and that the union of the two sexes gives only a stimulus, and brings into view forms that had existed since the world began.
This hypothesis has attempted to explain a thing that is unknown by what must for ever remain incomprehensible to the human mind in its present state. It appeals absurdly from observation to conjecture; and supposes that bodies which are originally brought into view, which are daily augmented, frequently repaired, and sometimes renewed by organic action, do nevertheless in their first formation require an effort superior to what omnipotent power is able to perform by secondary agents.
Had the supporters of this hypothesis considered that many herbaceous plants produce new flowers when the first set are untimely cut off, that lobsters and many species of insects renew their limbs, and that certain polyps can raise so perfect vegetable forms as to puzzle the naturalist whether or not he should class them under plants; they would not surely have preferred such bounds to omniscient wisdom and almighty power, or declared with such confidence what the Author of Nature, to speak with the vulgar, must necessarily perform by his own hands, or what he may intrust to secondary causes regulated by his laws.
These philosophers will find it difficult to account in a very satisfactory manner for monstrous productions, and for those changes of structure and of form which for a while continue hereditary from the influence of habit. They object to others, that all the parts of a living body are mutually dependent on one another, and that they must necessarily have been coeval or existed at once. But though every attempt that has yet been made to ascertain which of the vital organs are prior and which posterior in a living body has proved unsuccessful, it has not been demonstrated that either themselves or their functions are coeval. It may, on the contrary, be proceeded plainly demonstrated from observation, that the lungs and the stomach do not begin to perform their functions so early as the heart and the vascular system; that the heart and its system perform their functions, even with some considerable changes, immediately after birth; that the vegetable tribes are without nerves; and that brain and nerves in the animal kingdom perform more and more of their functions as the system approaches towards maturity. It has even been shown that bones will unite, and the limbs of an animal continue to be nourished without nerves; that there is a principle of life in the blood; that the heart will act under other stimuli besides that of nerves; and that sound logic does by no means require us to suppose that the first actions of the fetal heart, or the punctum saliens, are owing to the influence of stimuli from the brain, or that the brain must have existed when the heart first moved.
Although the minuteness and transparency of the parts may prevent us from seeing the first gradual formation of the embryo, yet every observation corroborates the opinion that it is formed by secondary causes, and through the medium of organic powers.
It has been asked, whether or not is the embryo formed by the joint operation of the two sexes? or is it formed entirely by the one, and brought into action by a stimulus from the other? The former of these questions supposes that each of the sexes has a seminal fluid; that some mixture takes place in the uterus, and produces an embryo, in the same manner that a neutral salt affumes a certain and determinate form. The notion implies some general and confused idea of chemical combination; but does not bespeak a very clear head, profound reflection, or much acquaintance with the nature and properties of living bodies.
For a long time past the most rational physiologists have generally agreed that the embryo is formed gradually and slowly in one or other of the two sexes, not by chemical combination and mixture, but by a system of organs, directed by laws and prompted by stimuli, with many of which we are yet unacquainted.
From the great Hippocrates downwards to Aquapendens and Harvey, the credit of furnishing the fetal embryo was almost universally given to the females of those animals which are named oviparous. Among the viviparous, appearances were such, that the female was left to contemn it with the male. At last the eclat of Leeuwenhoek's discoveries seemed to put an end to all doubts entertained upon the subject. He very clearly saw through his microscope that very great and profusion of particles that move to and fro with amazing rapidity in the male semen. Upon this he embraced the doctrine of Hamme, who had seen them before, and supposed from their motions that these particles were not only animalcules, but the principles or rudiments rudiments of that animal in whom they were formed, and that they were deposited in the uterus of the female only to be nourished and augmented in size.
What raised suspicions against this theory were the numerous animacules discoverable by the microscope in other fluids, and that vast profusion of young embryos in those cases where never more than one or two arrive at maturity. It was an objection to it, that some females had been impregnated where the hymen remained unbroken, and where the vulva had been shut so closely as to leave only a passage for the urine. The male semen in these instances could have reached only the mouth of the uterus. It was another*, that in all birds which have no intrant penis the male semen is never sent farther than the mouth of the vulva, and that a single act of the male impregnates the whole eggs of the ovarium. A third objection is the pollen of flowers, which is not applied immediately to the seed, but often to a distant part of the vessel in which it is contained. A fourth may be taken from frogs and fishes, and all those animals whose eggs are impregnated after emission. And, lastly, Haller had observed the pullet completely formed in those eggs that were not fecundated.
Supposing animacules in every kind of prolific semen, yet it frequently happens that this semen undergoes a change before it can be applied to the embryo. The semen of the frog is dissolved in water; and that which is injected disappearing suddenly after coition, would seem to intimate, that in those animals which have been examined it had met with a solvent somewhere in the uterus, and produced its effect after the change. It is now, we believe, pretty generally known, that the embryo does not commence its existence in the cavity of the uterus. De Graaf observed it on its passage down the Fallopian tube; he saw the place where it first began in the testicle of the female; and cases have occurred where it has missed the Fallopian tube, where it has fallen into the abdomen, where the placenta has been formed, and the foetus has grown among the viscera of the lower belly.
From these facts it has been concluded, notwithstanding some feeble objections, that the female testicles are real ovaries containing eggs; that these eggs are brought into action by the stimulating power of the male semen, which is sometimes thrown into the cavity of the uterus, sometimes applied only to its mouth, and sometimes sprinkled over the egg after emission.
The principal difference, therefore, that occurs between oviparous and viviparous animals, considered as such, appears to be this: the former are accustomed to eject their embryo before it escapes from the membranes of the egg; the latter retain it long in the uterus until it acquires a considerable size, until the membranes can hold it no longer, and then eject it when the membranes are burst. A plant is oviparous when it yields seed; viviparous when it produces a gem, a bud, a bulb, or an eyed root. The membranes of the seed being removed, an incipient embryo is seen through the microscope.
Some animals, according to the season, eject the some embryo inclosed in its membranes, or retain it in the uterus till the membranes are broken. These are oviparous and viviparous, the animals which are said to be oviparous at one period and viviparous at another. The spider-flies retain their young till they be as large as the natural size of their own bodies, and have undergone all their transformations within the expanfile membranes of the egg, and an uterus as expanfile as the stomach of a serpent.
In most cases generation requires a temporary union of two sexes; but it has been said, that in Senegal the sexes there is a species of shell-fish among whom this operation is the joint work of three individuals. In our own country, too, three frogs are frequently observed adhering together, though the labours of the third have generally been thought more officious than necessary. In some animals the sexual union is almost instantaneous. It constitutes nearly the business of life in the last stage of the ephemeron; and the male both of the frog and toad often continues on the back of the female not for hours and for days only but for some weeks. Upon examination it has been found, that with his fore-feet he affixes the female to protrude her eggs through the windings of the oviduct; and when they at last arrive at the anus, a species of the toad has been observed to draw them out with his hind legs. These animals were probably the first of the masculine gender who practised this art. But due honour has not been ascribed to the discoverers. In former days, the generous and grateful spirit of the ancients made them ready to acknowledge their obligations to different animals for the arts of bleeding, clattering, and purging; but such is the degeneracy of modern times, that many write only to claim the discoveries of others. On this account we ought not to wonder that many accoucheurs, in publishing encomiums on their own merit, have inviolably concealed the superior pretensions of the obstetrical toad.
Among all living bodies the two sexes are generally similar; and the male sex generally distinguished by superior strength, beauty, and courage. The law, however, of the two sexes does not hold universally. The females of some carnivorous animals, who are left by the male to provide for their offspring, are larger, stronger, and more ferocious than he. Among some insects the male and female have no similarity even in form. The male of the glow-worm is a beetle, which flies in the dark, and is attracted not by the form, but the brilliancy of his mistress (g). The female gall insect is a large mass like a vegetable
(g) Such glowing beauty allures enemies as well as lovers. "In Jamaica, in some season of the year, (says Dr Darwin), the fire-flies are seen in the evenings in great abundance. When they settle on the ground, the bull-frog greedily devours them; which seems to have given origin to a curious, though cruel, method of destroying these animals: If red-hot pieces of charcoal be thrown towards them in the dusk of the evening, they leap at them, and, hastily swallowing them, are burnt to death." Botanic Garden. From this fact the romantic moralist and spiritualist might derive some hints for amusing declamation; and in their diffusives might plausibly demonstrate, that in most cases beauty is fatal to the object beloved, to the lover, and destroyer. vegetable excrecence, without locomotion; the male a small fly full of activity. The one is as unlike to the other as a Harry to a Venus, and as disproportionate in point of bulk as a horse to an elephant.
In many animals the distinctions of sex are concealed in the body. When any of their parts are placed externally, or protruded occasionally, the male parts are usually prominent, and the female hollow, in order to receive them. In the acari, however, in many flies, and a few hornets, the case is reversed; the female parts suffer erection, and the male parts are open and hollow for their reception.
The external situation of these parts is very much varied in different animals. In many worms it is near to the head. It is often upon the side of the snail; near to the breast in the female of the dragon-fly. It is at the extremity of the antennæ in the male spider. The vulva enters from the rectum in birds. Its common situation in most animals is well known.
The male penis, where there is one, is sometimes found to enter the vulva, and sometimes not: it is sometimes imperforated, sometimes forked, sometimes double, sometimes fleshy, sometimes bony, sometimes straight, sometimes winding spirally like a screw, sometimes with a knob and sometimes with a point at its extremity, according to the kinds and varieties of animals.
Few individuals have more than one sex. Many snails, however, are androgynous, and have two. In copulation they perform the office of two sexes, and are mutually impregnated. This circumstance has often led the sensualist to wish that he were a snail. With equal reason the Epicure might wish to be one of those worms that imbibe by absorbents, and suck in nourishment by a thousand mouths. The organs employed may be more in number, the continuance of their function may be much longer, and yet the gratification may be less. The disagreeable beauty can afford a million of pleasures to her lover which no snail or sensualist enjoys, and which prostitution can never yield.
The male and female parts of the vegetable are sometimes both on the same flower, sometimes on separate flowers, and sometimes even on different plants of the same species. Besides the flower, another organ of generation is found in vegetables. This is the corona, from which the buds and branches proceed. It is a substance between the pith and the ligneous circles, and from which the diametral insertments diverge.
The corona is most conspicuous at the time when it sends forth shoots. The flower comes forth only at the time when the seed is to be formed; and the testicles and ovaries of those animals which procreate only at stated periods are diminished in size, and sometimes disappear, till the genital season. Even some females, when they cease to be prolific, as the pheasant, for instance, assume many marks of the other sex, as if their former sex had been assumed only for a while, and to answer some temporary purpose.
In all animals the incipient embryos are perhaps neuters, and the sex determined according to the predominancy of the male or female stimulus on the parts. It would not a little confirm this opinion, were the observation to be well founded, that certain bulls are very apt to beget males and others females, and that certain cows which have females always when they are young bring forth males when they grow old. The different proportions of males and females in different climates might also serve to illustrate this doctrine. It is no perhaps objection to it that the order of male and female births in the same family is often irregular. The proportional force of the two stimuli will naturally be different at different times. It may depend on the quantity or quality of the fluid secreted, upon the difference of ardour in the parties, on the fancy, the passions, the particular state of the system at the time, and a thousand circumstances, besides the age, and the usual or general habit of the body. We mean only to infer at present, that wherever a male or female is produced, the stimulus of that particular sex, whatever was the cause, had during the time of coition and conception acquired the ascendency over the parts that were to become sexual in the embryo. We cannot so readily answer the question, Why the offspring should possess the form and dispositions of one parent, and the sex of the other? In this case the different stimuli may have acted differently on different parts; in the case of hermaphrodites, which are very common in the horse, the ass, the cow, and the sheep, the two parents seem to divide the form, the sex, and the dispositions, equally between them.
The particular cause which excites the orgasmus in the female organs is not ascertained. That viscus orgasmus, fluid which young lascivious females eject when fond of the male, is chiefly a secretion from the glands of the vagina, the mouth of the uterus, and the neighbouring parts. In some respects it appears to be similar to those periodical discharges of females which frequently assume the erect posture; and these discharges being usually discontinued during the times of pregnancy and suckling, we must suppose that it is a portion of that fluid which nature has prepared for the use of the fetus. These discharges are always a proof that the female has arrived at the age of puberty; that her ovary is now performing its office; and that she is disposed to propagate her kind. Whatever be the cause of the female orgasmus, it is often so strong as to counteract the natural effects of the seminal fluid, and prevent impregnation. For this reason, few young and lascivious females conceive immediately after their marriage; and after coition, therefore, in cattle, it is sometimes a practice to beat the female, to plunge her in water, to weary her with running, and to use other means to prevent the return of the sexual desire.
In man, and some of the nobler animals, the influence of the organs of generation is unequal; fancy overpowers the natural effects of the seminal fluid, and prevents impregnation. For this reason, few young and lascivious females conceive immediately after their marriage; and after coition, therefore, in cattle, it is sometimes a practice to beat the female, to plunge her in water, to weary her with running, and to use other means to prevent the return of the sexual desire.
In man, and some of the nobler animals, the influence of the organs of generation is unequal; fancy overpowers the natural effects of the seminal fluid, and prevents impregnation. For this reason, few young and lascivious females conceive immediately after their marriage; and after coition, therefore, in cattle, it is sometimes a practice to beat the female, to plunge her in water, to weary her with running, and to use other means to prevent the return of the sexual desire. did inquirer from drawing very hasty conclusions.—The queries of Fienus (n) concerning the powers of this mental faculty are important and curious, and might be of use in directing our researches; but they ought to be answered by accurate experiments, and not by acute metaphysical reasoning and historical anecdotes that are ill authenticated.
To prevent a confusion of genera and species, animals are generally restricted by propensity to their own kind; and the seminal fluids, besides being various in various animals, they cannot indiscriminately act as a stimulus on all female organs of generation. The changes of form induced by habit, which is owing itself to the influence of stimuli, will partly explain the manner in which the progeny is made to resemble the male. As the irritability of different parts is of different kinds, the stimulus will have a different effect on different organs; and in these cases where either genera or species are mixed, the parts which are most and least affected by the stimulus of the male will be obvious in the shape and form of the offspring.
We have hitherto spoken of generation as being performed by the temporary intercourse of two sexes; but the puceron is an instance where sexual distinctions are not always necessary. Even where they exist they are daily dispensed with in the vegetable kingdom. Plants grow from the gem, the bulb, the leaf, or the root.—They propagate by slips, by suckers, and by layers, and some of them multiply by spontaneous separation (i). In many animals the distinctions of sex are totally unknown. It has been observed, that insensory animacules multiply their species by continual divisions and subdivisions of their own body; that some polypes, by spontaneous separation, split transversely, some longitudinally, and that some send off shoots. When experiments have been made upon these animals, it has been discovered that the numerous and artificial divisions of their body or their head produce entire animals. Trembley learned that they might be engrafted upon one another, and produce monsters as wild and extravagant as poet or fabulist has ever dreamed of.
It was noticed already that the alimentary canal of some animals distributed nourishment through the whole body without the intervention of circulating vessels, and that the vital organs of vegetables were generally diffused through the whole system. The case is the same in polypes as in plants. Every part is a miniature of the whole. It is found to have similar organs of digestion, of respiration, of circulation, and of generation. In perfect animals all the parts are more dependent on one another; the vital organs have distinct situations, and their powers are concentrated in distinct places. The arm of a man has no heart; it has no lungs; it has no stomach, and no organs of generation; but the branch of a tree has as complete a system of organs as the trunk itself, and is as independent of that body from which it grew as the gait is independent of the stock.
The several parts of perfect animals all contribute to make one whole; the several parts of a plant or polype, when united together, form only a congeries of plants and living bodies. These facts contribute to explain the principal phenomena in this mode of propagation.
Sect. XIII. Sleep.
Sleep is rather an affection of mind than a property of body, and is therefore more naturally a subject of metaphysics.
(n) The small work of Fienus to which we allude is intitled De Viribus Imaginationis Tradatus. The following questions serve to give an idea of its contents, and are named Index Questionum hujus Libri.
Question I. An anima habeat vim agendi in ullum corpus?
II. In quae corpora agere possit, et qua actione?
III. Per quas potentias illos motus et actiones exercet?
IV. An anima agat aliquid per potentiam imaginativam?
V. An phantasia possit ullum corpus movere localiter?
VI. An possit alterare?
VII. An phantasia possit vim ullam acquirere ab influxu coelorum?
VIII. An ergo phantasia nullam habeat vim agendi?
IX. Per quas potentias phantasia corpora immutet?
X. Quid possit in corpus proprium, et specialiter, an possit in eo creare morbos?
XI. An possit morbos creare?
XII. Quid possit in alienum externum?
XIII. Quid possit in alienum propinquum seu foetum?
XIV. Quomodo et qua ratione foetum immutet?
XV. Quomodo possit conformaticem dirigere?
XVI. Quam imaginatio habeat illam signandi potestatem? quae non?
XVII. Cur non omnis imaginatio quam animi passiones sequuntur signat?
XVIII. An omnes animi passiones signat?
XIX. Quam imaginatio signet, an tantum matris an etiam patris?
XX. An etiam brutorum imaginatio signet?
XXI. Quo tempore signet, an tantum graviditatis, an etiam conceptus?
XXII. Quantum permutationem possit in foetum inducere, et quas signaturas possit causare?
XXIII. Cur phantasia non semper imprimet in foetum res imaginatas eodem modo, sed sepe tam diversis?
XXIV. Cur non eadem semper parti sed diversis notis inducuntur?
(i) As the house-leek and some grasses. metaphysics than of physiology. This affection is often induced by fatigue and exercise; and several persons, when they are weary and no longer able to move their limbs, say they are exhausted. Though the word exhausted, in this expression, has seldom any precise meaning, it seems, however, to have been the means of suggesting a theory with regard to sleep. This theory supposes that sleep is occasioned by the exhaustion of irritability in the living system; but it seems to be founded on very limited and partial observations, or rather has been formed, like a great many others, prior to any observations at all, and afterwards tortured to account for facts which it does not comprehend. It does not account for the periodical returns of sleep, for the almost unremitting drowsiness of infants, and for that little lethargic inaction so often attendant on old age. When no exhaustion of irritability can well be supposed to have taken place, the propensity to sleep on many occasions becomes irresistible, from the effects of monotonous speaking, from stillness, darkness, or from the sameness of scenery around us; and when one stimulus, after long application, can rouse no more (a plain proof that the irritable principle is by no means exhausted), another stimulus that is less powerful in ordinary cases is accompanied with excitement.
Of these phenomena, we frankly confess that we can assign no physical cause that is satisfactory. It is easy, however, to see the intention which nature has in view by inducing sleep. It has long been observed, that in all living bodies there is a continual waste and repair, or, to speak with more precision and accuracy, one process of assimilation and another of dissolution constantly taking place in all the different parts of the system. It is also true that this assimilation, when the body is healthy, predominates in youth; that dissolution prevails in old age; and that the two are nearly on a par during the vigour and meridian of life. Another fact which admits of demonstration is, that a gentle and moderate exertion of mind and body will promote both. And lastly, it is certain that immoderate exertion in either respect, or any exertion that is not suited to our strength, habits, or period of life, prevents assimilation, hinders dissolution; and that the means which nature employs to restore the balance is usually by inducing a state of sleep.
When the balance is restored, and all the parts are again repaired for discharging their office, man awakes; but his waking period is of short duration. If appetite or passion do not engage him in some pursuit, if his mind be not occupied with some object, or if no stimuli be applied from without. This period seems chiefly intended for collecting food, and for being employed in those exertions which promote respiration, digestion, absorption, circulation, and secretion; while sleep, after the food is collected, assists nutrition, and promotes assimilation throughout the system. If what is the natural food of the species cannot be collected by the plant or animal in a short time, the period of sleep is proportionally restricted. If the food received be difficultly assimilated, the period of sleep is proportionally extended. If the food be not prepared for assimilation, the sleep is disturbed. If it be difficultly prepared by the organs, the active exertions are more vigorous; if easily prepared, they are more feeble. If it be collected during the day, the sleep is in the night; if collected in the night, the sleep takes place during the day; and all living bodies are directed by nature to select that time and species of food which is most suited to their nature, their habits, their circumstances, and age.
To favour nutrition, not only the body, but even the mind, must be allowed to indulge in rest. The child sleeps, and his mental faculties are under restraint, that those functions employed in nutrition may not be disturbed. The mental faculties are still feeble in a more advanced period of life; and the moderate exertions of mind and body which are natural to youth are chiefly such as favour the preparatory organs of the system, and promote growth; but the active and vigorous exertions of manhood, considered with respect to mind or to body, soon cause dissolution to preponderate in the scale, and old age becomes listless, inactive, and drowsy, and the mind returns to childhood or dotage, because living bodies are known to accommodate themselves to circumstances, and because the prevailing dissolution is retarded by the frequent returns of rest and of sleep, which favour so much the assimilating powers, counteract re-absorption, and oppose decay.
During sleep the irritable principle is more languid, and all the senses are more obtuse. The mind then is withdrawn to its rest, and does not attend to stimuli from without. The same happens when the mind is absorbed in profound thought; but profound thought is hurtful to the system. The mind then is engaged in pursuits peculiarly its own, and is less attentive to the calls of nature. In the time of sleep it withdraws seemingly, nor so much for its own sake as that of the body, which then being freed from the interruption of voluntary motions, all those organs which act spontaneously can more easily discharge their functions.
For the best of reasons, the mind is not allowed to judge for itself when it is proper to eat, to drink, to sleep, to wake, and to propagate the species. These and the like are offices too important to be wholly intrusted with a being of so very limited intelligence. In all these cases, it is therefore directed by certain propensities resulting from the body in consequence of stimuli or organic structure. Being often amused with thoughts and ideas on those objects which are purely intellectual, as the notes of memory, the forms of fancy, and its own operations in the way of reasoning; being invested by some little power in reasoning, calming, and regulating the passions, the desires, and appetites; and therefore having the command of all the voluntary movements of the body; it sometimes neglects its charge of the system, destroys it sometimes by excessive indulgence, and sometimes employs it in accomplishing ends peculiarly its own. One should imagine that the mental principle in the lower animals should occasion but little disturbance to the system; yet it has been observed that geese fatten sooner in the dark than they do in light, where the mind is entertained with varieties of objects; and this circumstance will partly explain why man does not fatten so regularly as the brute, and why castration, which prevents so much anxiety and passion and exhausting efforts, assists growth and the organs of nutrition. The venereal stimulus, for this reason, is not strongly felt at a very early period of youth, nor is very troublesome in old age. In the former case it would would prevent the growth of the system; in the latter it would hasten its dissolution.
The natural returns of waking and sleeping may be altered by the presence or absence of stimuli, and are curiously affected by the influence of habit. Although the commencement of one of these periods happen to be changed, the commencement of the other will continue as before. If a person be accustomed to sleep precisely at nine in the evening, and to rise again at six in the morning, though his sleep in the evening may now and then be kept off till twelve, he will waken at six; and though continued by darkness, quietness, or such like causes, till the day be advanced, it will recommence in the evening at nine. The state of physiology is such at present that we cannot assign any precise physical cause for the natural kinds of sleeping and waking, or for their regular periods of return. As for the causes which occasion morbid sleeping and waking, we refer our readers to books on pathology.
Plants too have been said to sleep. At the approach of night, many of them are observed to change their appearances very considerably, and sometimes even to such a degree as scarcely to be known for what they were before. These changes happen principally to the leaves and the flowers. During the night, many leaves, according to the nature and genus of the plant, are seen to rise up, to hang down, or to fold themselves in various ways for the protection of the flowers, the buds, the fruits, or young stems; and many flowers, to escape a superabundance of moisture, to hang down their mouths towards the earth, or wrap themselves up in their calyxes. It was mentioned already, that these phenomena are owing to stimuli acting from without: we may add here, that most of the motions are performed at the joints where the leaves and petals articulate with the stem. A period of rest is as necessary to plants as sleep is to animals. The irritable principle cannot act long under the influence of the same stimulant, except at intervals; and the rapid growth observable in plants during the night, is a strong proof that the organs employed in assimilation had been disturbed in discharging their functions during the day, when exposed to the actions of heat and light and of other stimulants.
Sect. XIV. Death.
Death is the cessation and total absence of the living principle in organized bodies. It is sometimes imitated by sleep and swoons; and a state of torpor in many instances can hardly be distinguished from it. Several mosses and a few animals, as the ears of blight-
(x) Father Gumillo a Jesuit, and the Indians of Peru, says Dr Fowler, are quoted by Fontana, on the authority of Bouguer, as speaking of a large and venomous snake, which being dead and dried in the open air or in the smoke of a chimney, has the property of coming again to life on its being exposed for some days to the sun in stagnant and corrupted water. But, adds the Doctor, it would almost require the credulity of an Indian to credit the testimony of the Jesuit. Experiments and Observations relative to Animal Electricity, by Richard Fowler.—With regard to this report, we shall only observe, that the snake would not readily return to life after it was dead; but if the Jesuit meant only that it recovered after it was dried, and its several functions had been suspended, we must say, that if his report be not sufficiently authenticated, neither has it been sufficiently disproved. be somehow performed, and then die. But when all the organs are fully evolved and have discharged, or have continued for the usual time capable of discharging, those offices for which they were intended; diffusion commences, the assimilating organs begin gradually to lose their tone, and the reabsorbents carry off more from the different parts than what they receive in the way of nutrition: the irritable fibre then becomes rigid; the membranes and cartilages begin to ossify; the bones grow harder; the smaller vessels collapse and disappear; the parts no longer are obedient, as before, to the action of stimulants; and death ensues.
Some, in order to account for this event, imagine that the body receives at first a certain portion of irritability, and continues to live till that be exhausted: but this theory explains nothing; and without pretending to a great deal of foresight, we will venture to predict that for all the irritability which it has, it will not be distinguished for its longevity.
With regard to the periods by which the life, the functions, and diseases of living bodies are so frequently regulated, and which periods may sometimes be varied but not evaded, the most prudent language that, signed for perhaps, can be adopted in the present state of physiological science is this of the Divine, That the God in the phenomena who formed us hath numbered our days, determined our times, and prescribed the limits of our existence.
The following Table may be considered as in some respect a summary view of the foregoing Sections, and as a Supplement to the Table of D'Azyr.
| Diffused through the system. | |-----------------------------| | Confined to one place. | | Situated externally. | | Situated internally. | | In the course of circulation.| | Not in the course of circulation.| | Within or without the course of circulation at pleasure.| | Without tracheæ (m). | | With tracheæ ramified through the system where the respiratory organs are generally diffused.| | —— not ramified through the system where the respiratory organs are confined.| | —— formed by rings. | | —— by segments of rings on one side, and a membrane on the other.| | —— by continuous rings running spirally like a screw.| | —— admitting air by one entrance.| | —— by several entrances. | | —— wholly concealed in the body.| | —— partly projecting from the body.| | —— opening at the head. | | —— at the opposite extremity.| | —— upon one side. | | —— upon both sides. |
| Without teeth. | |-----------------------------| | With teeth in the mouth. | | —— in the stomach. | | —— stones or artificial teeth in the stomach.| | —— glands in the mouth for secreting a liquor to be mixed with the food.| | —— pouches in the mouth where the food is kept and moistened.| | —— a sac or bag where the food is kept and moistened.| | —— a membranous stomach. | | —— a muscular stomach. | | —— an intermediate stomach. |
| Without a cæcum or blind gut.| |-----------------------------| | With a cæcum. | | —— two cæca. | | —— three cæca. | | —— four cæca. | | —— one entrance or mouth. | | —— many entrances by absorbents.|
(1) The gentlemen of the French Academy, who have been attentive to mark the number of lobes in the lungs and livers of different animals, have sufficiently demonstrated, by the facts which they relate, that many of those physiological conclusions which have been drawn from the number of lobes in these two viscera, are just as delusive as many of those which have been drawn from the number of lobes and the different tubercles found in the brain.
(2) Where the respiratory organs are situated externally. Plants have many alimentary canals (n).
Some polypes have alimentary canals that branch through the body.
The alimentary canals of plants, of some polypes, and worms, distribute the fluids without the aid of a circulating system.
By vessels beginning from the alimentary canal, - from the cavities. - from the surface. - veins in the penis and placenta. - reabsorbents originating from all the parts of the system.
No circulating system. A circulating system with one heart. - a heart for distributing the blood through the respiratory organs, and an artery for distributing it through the system. - one heart for the respiratory organs, and one for the system, both in one capsule. - two hearts for the respiratory organs, and one for the system. - a pulmonary heart, or a heart for the respiratory organs in the course of circulation. - a pulmonary heart within or without the course of circulation pleasure. - a heart situated in the breast. - near to the head. - in the opposite extremity.
By the alimentary canal. - the lacteals. - the respiratory organs. - the circulating system. - the cellular membrane. - glands.
And by the several parts in which it becomes finally assimilated.
By vessels. - exhaling vessels. - excretory organs. - organic pores. - glands.
And by all the parts of which the system is composed.
Which are scaly. - shelly. - membranous. - cornaceous. - cretaceous. - ligneous. - covered with down. - hair. - prickles. - feathers. - a viscid matter.
change their colour. their covering. are changed themselves.
(n) The subterraneous bulbs, the fleshy parts of the roots, and certain cups and vesicles which contain water, serve often as reservoirs of food to the plant, although for various reasons we have not ventured to call them stomachs. Stomach would be a vague and unmeaning word were it applied even to all those reservoirs of water or secreted fluids which we find in fishes, and by which some of these animals are preserved alive on the dry shore till the tide return.
(o) There seems to be a want of precision in classing bones with integuments, or integuments with bones, as
8. Irritability.
The irritable principle affected
- By stimulants invisible. - unknown. - unthought of. - the nervous influence. - light. - heat. - moisture. - electricity. - salts. - gases. - bodies that act mechanically.
9. Motion.
Locomotion performed
- By legs. - wings. - fins. - the tail. - organs which fall not properly under these descriptions. - the springiness of the body or of some part of it. - contrivances which fit living bodies for being moved by foreign agents (p).
Vol. XIV. Part II.
4 Y
10. Habit.
is done in D'Azyr's table. Comparatively speaking, bones are confined to a few genera of living bodies, and are never subject to periodical changes like the integuments or cuticular coat of the alimentary canal in some animals.
For the sake of perspicuity, it could have been wished that either anatomists or physiologists had defined bones in a manner different from what they have done, and as far as possible avoided those loose and inaccurate expressions which disgrace science; for some speak of animals having their bones, by which they mean shells, on their outside, and the muscles within them. Some speak of solid and compact bones that were once cartilages, membranes, nay a mere jelly; and some speak of bones in general as the hardest, most solid, and most inflexible parts of the organized body. From all this we are led to infer, that integuments, if hard, solid, and inflexible, may be called bones; that the heart and blood vessels, if converted into a hard, solid, and inflexible substance, may be called bones; and that a jelly, a membrane, or a cartilage, if it can be supposed that in the course of nature they will become hard, solid, and inflexible, may likewise be called bones. But certainly if hardness, solidity, and inflexibility, be to constitute the characteristics of bones in a living body, however often we may be necessitated to include shells, wood, horns, and stony concretions, under that denomination, we can never with propriety speak of bones that are cartilaginous, membranous, or even a mere jelly.
These expressions might be proper enough were ossification considered merely as a natural or accidental circumstance, and were bones defined to be those internal parts of an animal which are intended by nature to form what is meant by the skeleton in its usual sense. These parts, we know, after passing through the forms of jellies, membranes, and cartilages, often become hard, solid, and inflexible, from ossification; a species of induration which is natural to the parts which form the skeleton of some animals, an induration which occasionally is extended to other parts, which sometimes exhibits the appearance of crystallization, and in many respects is different from the manner in which the wood of vegetables and the shells of animals become hard.
Ossification does not interfere so much as may be commonly imagined with the structure of bones: the structure of bodies may often be similar, and yet their mode of induration be different. Bones have been observed to consist of laminae, or plates like shells, and cylindric bones of concentric circles like wood. The concentric circles of wood have been found to consist of indurated membranes, which they receive successively from the bark; and Swammerdam discovered that the shells of some fishes were composed of laminae that consisted likewise of indurated membranes, or hardened cuticles, that had been successively furnished by the body. It has thence been supposed that bones, though hardened in a different manner, are of a structure nearly similar to that of some ligneous bodies and shells, and that their laminae in many instances consist also of indurated membranes, supplied successively by the periosteum when it is present. When it is absent, nature, which accommodates herself to circumstances, can form the bone in another way, and afterwards cover her new productions with a periosteum. For many excellent physiological observations on bones, we refer our readers to the Osteology of the late Dr Monro, and particularly to the volume already published of Mr Bell's System of Anatomy.
(p) The pulp which surrounds seeds is often the means of their propagation. Animals swallow the seeds for the sake of the pulp; and the seeds remaining indestructible, are carried to a distance, and discharged with the feces. To respiration. — digestion. — absorption. — circulation. — nutrition. — secretion. — integumation. — irritability. — motion. — transformation. — generation. — sleep. — death. — form. — size. — climate. — propensity. — the healing of parts that are morbid. — the renewal of those that are broken off.
By a change of proportion among the parts. — of their form. — throwing off old parts. — an addition of new ones of a different use, structure, and form. — a change of the whole form together. — of qualities, propensities, manners.
By the temporary union of two sexes. — the spontaneous separation of parts. — organs situated in the breast. — in the side. — near to the head. — in the opposite extremity. — an intrant organ of the male and a recipient organ of the female. — an intrant organ of the female and a recipient organ of the male. — the stamens and pistils of flowers. — the seminal secretion of the male thrown into the organs of the female. — sprinkled at the entrance of the female organs. — thrown upon them from a distance. — transported to them by the winds. — sprinkled on the embryo after emission. — dissolved in a fluid secreted by the female before it can rightly perform its office. — dissolved in water. — dissolved perhaps sometimes in air, as in the case of dicotyledonous plants, where it probably acts like an aroma.
By quietness. — the absence of stimuli. — the sameness of stimuli when long continued. — deficient assimilation. — deficient irritability, which is owing sometimes to the weakness, inattention, or confined powers of the mental principle.
After hours. — days. — weeks. — months. — seasons. — years. Not till after centuries.
All living bodies are much exhausted after performing the act of generation, and many of the inferior plants and animals begin immediately to sicken and decay. We conclude by confessing, that concerning many uses of the parts, and concerning different species of variety in the form, structure, and position of the organs, much, after all, is still reserved for further reading, for farther observation, and for future physiological arrangement.
PIA
PHYTOLACCA, POKEWEED, or American nightshade, in botany, is of the decidua icoandria clas of plants. It grows naturally in the province of Virginia in America. It hath a thick, fleshy, perennial root, divided into several parts as large as middling parsnips. From this rise many purple, herbaceous stalks, about an inch thick, and six or seven feet long, which break into many branches, irregularly set with large, oval, sharp-pointed leaves, supported on short footstalks. These at first are of a fresh green colour, but as they grow old they turn reddish. At the joints and divisions of the branches come forth long bunches of small bluish-coloured flowers, consisting of five concave petals each, surrounding ten stamens and ten styles. These are succeeded by round depressed berries, having ten cells, each of which contains a single smooth seed.
In Virginia and other parts of America the inhabitants boil the leaves, and eat them in the manner of spinach. They are said to have an anodyne quality, and the juice of the root is violently cathartic. The stems when boiled are as good as asparagus. The Portuguese had formerly a trick of mixing the juice of the berries with their red wines, in order to give them a deeper colour; but as it was found to destroy the flavour and to make the wine deleterious, the matter was represented to his Portuguese Majesty, who ordered all the stems to be cut down yearly before they produced flowers, thereby to prevent any further adulteration. The same practice was common in France till it was prohibited by an edict of Louis XVI., and his predecessor under pain of death. This plant has been said to cure cancers; but the truth of this assertion has not been indubitably proved, and does not appear very probable.
a discourse concerning the kinds and virtues of plants. See BOTANY, and Materia Medica.