In the same manner I have seen most of those minute animals move so swift that we could not account for it, without supposing such a provision in nature, which is really true, but cannot be seen till the animals grow faint for want of water; then, if we attend, we may with good glasses plainly discover them.

Method of discovering how to make their fins appear very distinctly, especially in the larger kind of animalcules, which are common to most vegetable infusions; such as the terrebella. This has a length body, with a cavity or groove at one end, like a gimlet: by applying, then, a small flake of the horse-hoe geranium (or geranium zone of Linnaeus), fresh broken, to a drop of water in which these animalcules are swimming, we shall find that they will become torpid instantly; contracting themselves into an oblong oval shape, with their fins extended like so many bristles all round their bodies. The fins are in length about half the diameter of the middle of their bodies. Before I discovered this expedient, I tried to kill them by different kinds of salts and spirits; but though they were destroyed by this means, their fins were so contracted, that I could not distinguish them in the least. After lying in this state of torpidity for two or three minutes, if a drop of clean water is applied to them, they will recover their shape, and swim about immediately, rendering their fins again invisible.

Fig. 3, 4, 5, 6, 7, 8. represent different species of animalcule infusoria, mentioned by Mr. Ellis as belonging to the genus of volvox of Linnaeus.

Fig. 3. represents the volvox ovalis, or egg-shaped volvox; at (b) and (c) it is expressed in its natural shape; at (a) the manner in which it becomes two animals, by separating across the middle. This was found in the infusion of hempseed; but is found in other vegetable infusions, particularly that of tea-seed.

Fig. 4. is the volvox torquilla, or wryneck. At (a) is represented its divided state; at (b) and (c) its natural state; this is common to most vegetable infusions, as is the following.

Fig. 5. is the volvox volutans, or the roller. At (a) the animal is separated, and becomes two distinct beings, each swimming about and providing for itself; this is often the prey of another species of this genus, especially while it is weak by this separation, not being so active for some time till it can recover itself. At (c) the animal appears to be hurt on one side; this impression in a little time is succeeded by another in the opposite side, as at (b), which soon occasions a division. At (d) is the side-view, and at (e) the front-view, of the natural shape of the animal.

Fig. 6. is the volvox oniscus, or wood-louse. At (a) is the natural shape of it, as it appears full of little hairs both at the head and tail; with those at the head, it whirls the water about to draw its prey to it; the feet, which are many, are very visible, but remarkably so in a side-view at (d). At (b) it is represented beginning to divide; and at (c) the animals are ready to part; in this state, as if in exquisite pain, they swim round and round, and to and fro, with uncommon velocity, violently agitated till they get afunder. This was found in an infusion of different kinds of pine-branches.

Vol. II. Part I.

Fig. 7. is the volvox terrebella, or the gimlet. This is one of the largest of the kind, and is very visible to the naked eye. It moves along swiftly, turning itself round as it swims, just as if boring its way. (a) and (b) are two views of its natural shape, (c) shows the manner of its dividing. When they are separated, the lower animal rolls very awkwardly along, till it gets a groove in the upper part. (d) represents one of them lying torpid, by means of the juice of the horse-hoe geranium, with its fins extended. This animal is found in many infusions, particularly of grapes or corn.

Fig. 8. is the volvox vorax, or glutton. This animal was found in an infusion of the Tartarian pine; it varies its shape very much, contracting and extending its proboscis, turning it to and fro, in various directions, as at a, b, c, d, e. It opens its proboscis underneath the extremity, when it seizes its prey. The least active animals, that have lately been divided, such as those at fig. 3. (a), and at fig. 4. (a), serve it as food, when they come in its way: there it swallows down instantly, as it is represented at fig. 8. h and i. At (f) it is ready to divide, and at (g) it is divided; where the hinder part of the divided animal has got a proboscis or beak, to procure nourishment for itself, and soon becomes a distinct being from the fore-part.

Thus we have given as full an account as our limits would admit, of the most curious kinds of animalcules that have hitherto been observed. We cannot, however, dismiss this subject, without taking notice of some of the most remarkable hypotheses which have been formed concerning their nature and origin.

Before the invention of microscopes, the doctrine of equivocal generation, both with regard to animals and equivocal plants of some kinds, was universally received; but generation, this instrument soon convinced every intelligent person, exploded. That those plants which formerly were supposed to be produced by equivocal generation arose from seeds, and the animals, in like manner, from a male and female. But as the microscope threw light upon one part of nature, it left another involved in darkness: for the origin of the animalcule infusoria, or of the spermatic animals already mentioned, remains as yet as much unknown as that of many other kinds was when the doctrine of equivocal generation reigned in full force.

The discovery of spermatic animalcules was thought supposed to throw some light on the mysterious affair of genera—discovery itself, and these minute creatures were imagined to concerning each of them individuals of the same species with the generation. parent. Here the infinite number of these animalcules was an objection, and the difficulty remained as great as before; for, as every one of these animalcules behoved to be produced from a male and female, to explain their origin by animalcular generation in the same manner, was only explaining generation by itself.

This hypothesis, therefore, having proved unsatisfactory, others have been invented. Mr. Buffon, particularly, hath invented one, by which he at once annihilates the whole animalcular world; and in this he hath been followed by several very ingenious philosophers. For a particular account of this, so far as it concerns generation, we must refer to that article; but as he gives such a particular account of his having examined the human form, that we cannot doubt of his accuracy, we shall here contrast his account with that of Mr. Lewenhoeck already mentioned. Having procured the seminal vesicles of a man who died a violent death, he extracted all the liquor from them while they were still warm; and having examined a drop of it with a double microscope, it had the appearance fig. 9. Large filaments appeared, which in some places spread out into branches, and in others intermingled with one another. These filaments clearly appeared to be agitated by an internal undulatory motion, like hollow tubes, which contained some moving substance. He saw distinctly this appearance changed for that fig. 10. Two of these filaments, which were joined longitudinally, gradually separated from each other in the middle, alternately approaching and receding, like two taut cords fixed by the ends, and drawn together in the middle. These filaments were composed of globules that touched one another, and resembled a chaplet of beads. After this, he observed the filaments swelled in several places, and perceived small globular bodies issue from the swelled parts, which had a vibratory motion like a pendulum. These small bodies were attached to the filaments by small threads, which gradually lengthened as the bodies moved. At last, the small bodies detached themselves entirely from the filaments, drawing after them the small thread, which looked like a tail. When a drop of the seminal liquor was diluted, these small bodies moved in all directions very briskly; and had he not seen them separate themselves from the filaments, he would, he says, have thought them to be animals. The seminal matter was at first too thick, but gradually became more fluid; and, in proportion as its fluidity increased, the filaments disappeared, but the small bodies became exceedingly numerous. Each of them had a long thread or tail attached to it, from which it evidently endeavoured to get free. Their progressive motion was extremely slow, during which they vibrated to the right and left, and at each vibration they had a rolling unsteady motion in a vertical direction.

At the end of two or three hours, the seminal matter becoming still more fluid, a greater number of these moving bodies appeared. They were then more free of incumbrances; their tails were shorter; their progressive motion was more direct, and their horizontal motion greatly diminished. In five or six hours, the liquor had acquired almost all the fluidity it could acquire, without being decomposed. Most of the small bodies were now disengaged from their threads; their figure was oval. They moved forward with considerable quickness, and, by their irregular motions backward and forward, they had now more than ever the appearance of animals. Those that had tails adhering to them, seemed to have less vivacity than the others; and of those that had no tails, some altered both their figure and their size. In twelve hours, the liquor had deposited at the bottom of the vial a kind of ash-coloured gelatinous substance, and the fluid at top was almost as transparent as water. The little bodies being now entirely freed from their threads, moved with great agility, and some of them turned round their centres. They also often changed their figures, from oval becoming round, and often breaking into smaller ones. Their activity always increased as their size diminished. In twenty-four hours, the liquor had deposited a greater quantity of gelatinous matter, which, being with some difficulty diluted in water, exhibited an appearance somewhat resembling lace. In the clear semen itself only a few small bodies were now seen moving; next day, these were still farther diminished; and after this nothing was to be seen but globules, without the least appearance of motion. Most of the above-mentioned appearances are shown fig. 10, 11, 12, 13, 14, 15, 16. Fig. 17 and 18 represent an appearance of the globules in another experiment, in which they arranged themselves in troops, and passed very quickly over the field of the microscope. In this experiment they were found to proceed from a small quantity of gelatinous mucilage.

From these experiments, Mr Buffon concludes, that what have been called spermatic animals, are not creatures really endowed with life, but something proper to compose a living creature; and he distinguishes them by the name of organic particles. The same individual kinds of animals he declares he has found in the fluids separated from the ovaria of females; and for the truth of this appeals to the testimony of Mr Needham, who was an eye-witness of his experiments. He also brings an additional proof of his doctrine from Mr Needham's observations on the milt of the calmar, a species of cuttle-fish. Here the spermatic animals, at least what on the milt have the only appearance of life, are vastly larger than any other creature, so as to be plainly visible to the naked eye. When magnified, they appear as at fig. 19, and 20. Their first appearance is at fig. 19, a and b, when they resemble springs inclosed in a transparent case. These springs were equally perfect at first as afterwards; only in time they contracted themselves, and became like a kind of screw. The head of the case is a species of valve which opens outward, and through which every thing within may be forced out. It contains, besides, another valve b, a little barrel c, and a spongy substance d e. Thus the whole machine consists of an outer transparent cartilaginous case a, the upper extremity of which is terminated by a round head formed by the case itself, and performs the office of a valve. This external case contains a transparent tube: which includes the spring, a piton or valve, a little barrel, and a spongy substance. The screw occupies the superior part of the tube and case, the piton and barrel are situated in the middle, and the spongy substance occupies the inferior part. These machines pump the liquor of the milt; the spongy substance is full of this liquor; and, before the animal spawns, the whole milt is only a congeries of these bodies which have sucked up all the liquor of it. Whenever these small machines are taken out of the body of the animal, and put in water, or exposed to the air, they begin to act, as represented fig. 19, and 20.; the spring mounts up, and is followed by the piton, the barrel, and the spongy substance which contains the liquor; and, as soon as the spring and the tube in which it is contained begin to issue out of the case, the spring plaited, and the whole internal apparatus moves, till the spring, the piton, and the barrel, have entirely escaped from the case. When this is effected, all the rest instantly follow, and the milky liquor which had been pumped in, and confined in the spongy substance, runs out through the barrel.

According to this account, the milt of the calmar contains no animalcules; and therefore we may from against the analogy conclude, that the small moving bodies which existence of are to be seen in the semen of other animals, are not animalcules. really creatures endowed with life. Mr Buffon extends the analogy still further; and concludes, that all the moving bodies which are to be found in the infusions either of animal or vegetable substances are of a similar nature. "To discover, says he, whether all the parts of animals, and all the seeds of plants, contained moving organic particles, I made infusions of the flesh of different animals, and of the seeds of more than 20 different species of vegetables; and after remaining some days in close glasses, I had the pleasure of seeing organic moving particles in all of them. In some they appeared sooner, in others later; some preserved their motions for months, and others soon lost it. Some at first produced large moving globules resembling animals, which changed their figure, split, and became gradually smaller. Others produced only small globules, whose motions were extremely rapid; and others produced filaments, which grew longer, seemed to vegetate, and then swelled and poured forth torrents of moving globules."

This last observation gave rise to a new system. Baron Munchenfien, perceiving that the last-mentioned moving globules, after moving for some time, began again to vegetate, concluded that they were first animals and then plants.—This strange hypothesis Mr Ellis has overturned in the paper already quoted; in which he asserts, that they are no other than the seeds of that genus of fungi called mucor or mouldiness, and that their motion is owing to numbers of minute animalcules attacking them for food. "Having (says he), at the request of Dr Linnæus, made several experiments on the infusion of mushrooms in water, in order to prove the theory of Baron Munchenfien, that their seeds are first animals, and then plants (which he takes notice of in his System of Nature, p. 1326, under the genus of chaos, by the name of chaos fungorum seminum), it appeared evidently, that the seeds were put into motion by very minute animalcules, which proceeded from the putrefaction of the mushroom; for, by pecking at these seeds, which are reddish, light, round bodies, they moved them about with great agility in a variety of directions; while the little animals themselves were scarcely visible, till the food they had eaten had discovered them. The satisfaction I received from clearing up this point, led me into many other curious and interesting experiments.

"The ingenious Mr Needham supposes these little transparent ramified filaments, and jointed or coraloid bodies, which the microscope discovers to us on the surface of most animal and vegetable infusions when they become putrid, to be zoophytes, or branched animals: but to me they appear, after a careful scrutiny with the best glasses, to be of that genus of fungi called mucor, or mouldiness; many of which Michelius has figured, and Linnæus has accurately described.

"Their vegetation is so amazingly quick, that they may be perceived in the microscope even to grow and feed under the eye of the observer.

"Mr Needham has pointed out to us a species that is very remarkable for its parts of fructification. (See Philosophical Transactions, vol. xlv. tab. 5, fig. 3, a, A.) This, he says, proceeded from an infusion of bruited wheat.

"I have seen the same species arise from the body of a dead fly, which was become putrid by lying floating for some time in a glass of water, where some flowers had been in the month of August 1768. This species of mucor sends forth a mass of transparent filamentous roots; from whence arise hollow items, that support little oblong oval seed-vessels, with a hole on the top of each. From these I could plainly see minute globular seeds issue forth in great abundance with an elastic force, and turn about in the water as if they were animated.

"Continuing to view them with some attention, I could just discover, that the putrid water which surrounded them was full of the minute animalcule; and that these little creatures began to attack the seeds of the mucor for food, as I have observed before in the experiment on the seeds of the larger kind of fungi or mushrooms. This new motion continued the appearance of their being alive for some time longer; but, soon after, many of them arose to the surface of the water, remaining there without motion; and a succession of them afterwards coming up, they united together in little thin masses, and floated to the edge of the water, remaining there quite inactive during the time of observation.

"As this discovery cleared up many doubts which I had received from reading Mr Needham's learned dissertation, I put into the glass several other dead flies, by which means this species of mucor was propagated so plentifully, as to give me an opportunity of frequently trying the same experiment to my full satisfaction.

"Lastly, These jointed coraloid bodies, which Mr Needham calls chaplets and pearl necklaces, I have seen frequently very distinctly. These appear not only on an infusion of bruited wheat when it becomes putrid, but on most other bodies when they throw up a viscid scum and are in a state of putrefaction. These, then, are evidently no more than the most common mucor, the seeds of which are everywhere floating in the air; and bodies in this state afford them a natural proper foil to grow upon. Here they send downwards their fine transparent ramified roots into the moisture which they float upon; and from the upper part of the scum, their jointed coraloid branches rise full of seed into little grove-like figures. When a small portion of these branches and seeds are put into a drop of the same putrid water upon which the scum floats, many of these millions of little animalcules with which it abounds, immediately seize them as food, and turn them about with a variety of motions, as in the experiments on the seeds of the common mushrooms, either singly, or two or three seeds connected together; answering exactly to Mr Needham's description, but evidently without any motion of their own, and consequently not animated."

Mr Buffon, however, is not content with denying life only to those beings where the signs of it are the most opinion of equivocal; but includes in the same rank of organic different kinds of animalcules, almost every animal too small to be discovered by the naked eye, and even some of those whole motions are evidently perceptible to the eye. "Almost all microscopic animals," says he, "are of the same nature with the moving bodies in the seminal fluids and infusions of animal and vegetable substances. The eels in past, in vinegar, &c., are all of the same nature, and derived from the same origin. There are, perhaps, as many beings that either live or vegetate, produced by a fortuitous assemblage of organic parti- cles, as by a constant and successive generation. Some of them, as those of the calmar, are only a kind of machines, which, though exceedingly simple, are very active. Others, as the spermatic animalcules, seem to imitate the movements of animals. Others resemble vegetables in their manner of growth and extension. There are others, as those of blighted wheat, which at pleasure can be made alternately either to live or die, and it is difficult to know to what they should be compared. There are still others, and in great numbers, which are at first a kind of animals, then become a species of vegetables, and again return alternately to their vegetable state. The eels in past have no other origin than the union of the organic particles of the most essential part of the grain. The first eels that appear are certainly not produced by other eels; but tho' they are not propagated themselves, they fail not to engender other living eels. By cutting them with the point of a lancet, we discover smaller eels issuing in great numbers out of their bodies. The body of this animal seems to be only a sheath or sac, containing a multitude of smaller animals, which perhaps are other sheaths of the same kind, in which the organic matter is assimilated into the form of eels.

Though we can by no means pretend to account for the appearance of these animalcules, yet we cannot help observing, that our ignorance of the cause of any phenomenon is no argument against its existence. Though we are not able to account in a satisfactory manner for the origin of the native Americans, we suppose Mr Buffon himself would reckon it absurd to maintain that the Spaniards on their arrival there found only organic particles moving about in disorder. The case is the very same with the eels in past. They are exceedingly minute in comparison with us; but, with the solar microscope, Mr Baker has made them assume a more respectable appearance, so as to have a diameter of an inch and an half, or two inches, and a length proportionate. They swam up and down very briskly; the motion of their intestines was plainly visible; when the water dried up, they died with apparent agonies, and their mouths gaped very wide. Were we to find a creature of the size of this magnified eel, gasping in a place where water had lately been, we certainly would never conclude it to be an organic particle, or a fortuitous assemblage of them; but a fish. Why then should we conclude otherwise with regard to the eel while in its natural state, than that it is a little fish? In reasoning on this subject, we ought always to remember, that, however essential the distinction of bodies into great and small may appear to us, they are not so to the Deity; with whom, as Mr Baker well expresses himself, "an atom is as a world, and a world but as an atom."—Were the Deity to exert his power for a little, and give a natural philosopher a view of a quantity of paste filled with eels, from each of whose bodies the light was reflected as when it passes through a solar microscope; instead of imagining them organic particles, the paste would appear like a little mountain, he would probably look upon the whole as a monstrous assemblage of serpents, and be afraid to come near them. Wherever, therefore, we discover beings to appearance endowed with the principle of self-preservation, or whatever else we make the characteristic of animals, neither the smallness of their size, nor the impossibility of our knowing how they came there, ought to cause us Animal-doubt of their being really animated.—At the same time, it must also be remembered, that motion is not always a characteristic of animal life, even though the moving bodies should avoid one another, or any seeming obstacle placed in their way. We know, that inanimate bodies, when electrified, will avoid others endowed with an electricity of the same kind, and adhere to those which have the opposite one. As we are by no means acquainted with the utmost powers of electricity, but on the contrary, from what we do know of it have all the reason in the world to conclude that it can produce effects utterly beyond our comprehension, it is impossible for us to know what share it may have in producing the motions observed in vegetable-infusions, or in the semen of animals.—We may also further observe, that though in Mr Ellis's experiment of the boiled potato he took it for granted that every seed of animal life would be destroyed by the boiling water, yet even this cannot be proved; nay, on the contrary, it hath been proved by undeniable experiments, that the human body itself hath endured a heat of 240 degrees of Fahrenheit (28 degrees above that of boiling water) without injury. The eggs of these animalcule might therefore be strong enough to resist the heat hitherto used in Mr Ellis's or any other experiment.

A considerable objection to the existence of animal-cules in the semen, or any other part of animal bodies, sometimes must arise from the total exclusion of air, which is found living necessary to the life of larger animals. Some instances, however, have been observed of large animals being found in such situations as they could not possibly have enjoyed the least benefit from the air for a great number of years; and in this state they have not only lived, but lived much longer than they would otherwise have done.

In Toulon harbour and the road, are found solid hard stones, and perfectly entire; containing, in different cells, secluded from all communication with the air, several living shell-fish, of an exquisite taste, called Dactylis, i.e. Dates: to come at these fish, the stones are broken with mauls. Also, along the coast of Ancona, in the Adriatic, are stones usually weighing about 50 pounds, and sometimes even more; the outside rugged, and easily broken, but the inside so hard, as to require a strong arm and an iron maul to break them: within them, and in separate niches, are found small shell-fish, quite alive, and very palatable, called Solenes or Cappe lunghe. These facts are attested by Gaffendi, Blondel, Mayol, the learned bishop of Suturara, and more particularly by Aldrovandi a physician of Bologna. The two latter speak of it as a common fact which they themselves saw.

In the volume for 1719, of the Academy of Sciences at Paris, is the following passage:

"In the foot of an elm, of the bigness of a pretty corpulent man, three or four feet above the root, and exactly in the centre, has been found a live toad, middle-sized, but lean, and filling up the whole vacant space: no sooner was a passage opened, by splitting the wood, than it scuttled away very hastily: a more firm and found elm never grew; so that the toad cannot be supposed to have got into it. The egg whence it was formed, must, by some very singular accident, have been..." been lodged in the tree at its first growth. There the creature had lived without air, feeding on the substance of the tree, and growing only as the tree grew. This is attested by Mr Hubert, professor of philosophy at Caen.

The volume for the year 1731 has a similar observation, expressed in these words:

"In 1719, we gave an account of a fact, which, though improbable, was well attested; that a toad had been found living and growing in the stem of a middling elm, without any way for the creature to come out or to have got in. M. Seigne, of Nantes, lays before the academy a fact just of the very same nature, except that, instead of an elm, it was an oak, and larger than the elm, which still heightens the wonder. He judges, by the time requisite for the growth of the oak, that the toad must have subsisted in it, without air, or any adventitious aliment, during 80 or 100 years. M. Seigne seems to have known nothing of the fact in 1719."

With the two foregoing may be clasped a narrative of Ambroise Paré, chief surgeon to Henry III., king of France, who, being a very sensible writer, relates the following fact, of which he was an eye-witness:

"Being (says he) at my feet, near the village of Meudon, and over-looking a quarry-man whom I had set to break some very large and hard stones; in the middle of one we found a huge toad, full of life, and without any visible aperture by which it could get there. I began to wonder how it received birth, had grown and lived; but the labourer told me, it was not the first time he had met with a toad, and the like creatures, within huge blocks of stone, and no visible opening or fissure."

Observations of living toads, found in very hard and entire stones, occur in several authors, particularly Baptista Fulgoza doge of Genoa, the famous physicians Agricola and Horitius, and lord Verulam: others give very specious accounts of snakes, frogs, crabs, and lobsters, being found alive, inclosed within blocks of marble, rocks, and large stones.

An instance similar to these, of the truth of which we have no reason to doubt, was observed in this country in the year 1773, where a large toad was found in the middle of a piece of coal having not the least visible crack or fissure.

Upon the whole, therefore, though philosophers are not yet able to discover how these minute creatures are produced; yet, that there really are animals much smaller than what we can discern with our naked eye, seems to be indisputable. The subject, however, is still evidently obscure, and will no doubt require the utmost attention of philosophers, as well as further improvements in the construction of microscopes, fully to investigate it.

Animalcula are said to be the cause of various disorders. The itch, from several experiments, is affirmed to be a disorder arising from the irritations of a species of animalcule found in the pustules of that ailment; whence the communication of it by contact from one to another is easily conceived, as also the reason of the cure being effected by cutaneous applications. On this foundation some have attributed the small-pox and measles, and infectious diseases; others the epilepsy, &c. to animalcules. Langius goes farther, and pretends to reduce all diseases in general to the same principle. A late writer at Paris, who assumed the title of an English physician, has done more. He not only accounts for all diseases, but for the operations of all medicines, from the hypothesis of animalcules. He has peculiar animals for every disease; scorbatic animalcules, podagrical animalcules, variolous animalcules, &c. all at his service. Journ. des Scav. tom. lxxii. p. 535, &c.

But as most discoveries in natural philosophy have laid a foundation for the warm imaginations of some men to form visionary theories, to the great prejudice of real knowledge; so those relating to animalcules have been drawn in, however improperly, to support the most whimsical and chimerical systems.

**Animalcules Invisible.**—Naturalists suppose another species or order of invisible animalcules, viz. such as escape the cognizance even of the best microscopes, and give many probable conjectures in relation to them. Reason and analogy give some support to the existence of infinite imperceptible animalcules. The naked eye, say some, takes in from the elephant to the mite; but there commences a new order referred only for the microscope, which comprehends all these from the mite to those 27 millions of times smaller; and this order cannot be yet said to be exhausted, if the microscope be not arrived at its last perfection. See further on this subject the article Microscope.