any substance which, acting on living bodies in small quantities, occasions serious disturbance of their functions, and may cause death. The science which treats of poisons is termed toxicology.

Poisons have been known from remote antiquity; but the notions entertained of their effects were generally fanciful and vague, so that it is often impossible now to discover what the poisons of the ancients really were. In modern times a great addition has been made to our knowledge of them, both as regards their number and their action; and it is only within the last thirty years that the nature and the varieties of their action have been studied scientifically and with success.

The number of poisonous substances now known is very great, and there can be no doubt that very many still re- main to be discovered, equally in the mineral, the animal, and the vegetable world, but more especially among vegetables. Numerous, however, as they are, they present many remarkable agreements in their effects or actions, so as to admit of convenient classification.

Some poisons produce no other effects besides what depend on the local injury they give rise to. Of these, some produce by their chemical properties absolute destruction of the textures to which they are applied; and the result depends less on the nature of the injury, than on the importance of the injured texture, and its sympathetic connection with other parts of the body. The mineral acids, such as sulphuric and nitric acid, and the mineral alkalis, potash or soda, are the best examples of this kind. Others, again, of those which act locally alone, produce inflammation, but not chemical destruction, where they are applied; and all the ordinary effects of inflammation may ensue; of which gamboge and colocynth are good illustrations. The action of the former description of local poisons does not differ essentially from that of mechanical injuries of the same textures; the action of the latter is almost identical with that of the natural causes of inflammation. A third description of local poisons merely produce a peculiar impression on the nerves of the part to which they are applied, without either destroying or inflaming its texture. But there is no pure instance of the kind yet known; all such poisons likewise act otherwise than locally. Opium and prussic acid are examples.

Other poisons, and these by far the most numerous, act upon remote organs and textures, on parts to which they are not, nay, cannot be, directly applied; and the effects of this kind are often developed without any appreciable signs of a direct local action. There is scarcely an important organ in the body which may not be brought thus under the influence of some poison or another. The brain is very often so affected, as by opium, belladonna, prussic acid, and charcoal fumes. The stomach and intestines are also frequently affected indirectly, as by arsenic. The spine is affected by nux-vomica, the kidneys and bladder by cantharides, the lungs by tartar-emetic, the heart by oxalic acid, the liver by manganese, the salivary organs by mercury, and many of the glands by iodine. Many poisons possess the property of acting on a great number of organs in this remote or indirect way, of which arsenic and mercury are perhaps the most remarkable instances. Arsenic introduced by the skin has been known to act on the stomach, intestines, kidneys, heart, the lining membrane of the eyes, nose, windpipe, and vagina, the nerves of voluntary motion, and the skin at a distance from its place of application. Physiologists are still in doubt through what channel these remote effects are produced,—some believing that the poison is carried in substance with the blood from the organ to which it is applied, into the parts on which it acts; others, that the operations are merely nervous, and consist of the transmission of certain local impressions along the nerves which communicate between one organ and another; and others, that both modes of action may exist, even for the same, and still more for different, poisons. Two facts, however, are clearly established, whatever theoretical deductions may be drawn from them: first, that very many poisons do enter the blood, and may be detected there; and, secondly, that these never enter except in very minute proportions; so that, unless very delicate tests are known for them, they may readily escape detection. It seems not improbable that some poisons are deposited by a species of election in particular organs; but of course their presence in the blood will give them access more or less almost everywhere, since there are few organs not traversed by blood-vessels, and minutely injected with blood.

The greater number of poisons produce their peculiar effects, through whatever texture they are introduced into the body. The effects of local poisons depend, as was stated already, on the texture to which they are applied; but the far more numerous denomination of poisons which act remotely, exert that action, to whatever part they are applied, provided they fairly enter the body. They enter the sound skin with extreme difficulty, unless in the form of gas or vapour, or with the aid of friction. But they act energetically through the surface of the true skin stripped of its cuticle, through the cellular texture under the skin, through the soft mucous membrane which lines the mouth, nose, ears, stomach, intestines, windpipe, and organs of generation, through the firm serous membranes which line the interior of the belly and chest, and also when introduced directly into the blood-vessels, more especially into the veins. They generally act with greatest energy when injected into the blood directly, or when introduced into the cavernous cavity of the chest or belly; but if they operate in very minute doses, their effects are scarcely less prompt when simply thrust into a fresh wound, or under the skin; and there is no way in which they exert their action with more swiftness and energy, than when inhaled into the lungs, provided they assume the form of gas or vapour. For the most part their activity is greatest when applied to organs and textures where absorption is most prompt.

The action of poisons is greatly modified by an infinite variety of collateral circumstances, without a thorough knowledge of which toxicology cannot be well understood, either as a branch of physiological science, or in its practical bearings on medical practice, as well as medical jurisprudence. These modifying circumstances cannot be accurately laid down here, but the most important are the following: quantity or dose, chemical or mechanical form, the texture directly acted on, habit, and peculiarity of constitution, either natural or induced by disease. By all of these causes the effects of poisons may not merely be altered in degree, but likewise even modified in kind, or entirely neutralized. 1. Most substances which are poisonous in moderate doses, are innocuous in small quantity; but some are amazingly energetic even in very minute quantities,—such as prussic acid or strychnia, the active principle of nux-vomica, either of which may prove fatal to a man in favourable circumstances in the dose of one grain,—or still more the poisonous secretion of venomous snakes, or the secretions of the human body in some diseased states, which will prove fatal in quantities inappreciably small if introduced into a wound. 2. As to mechanical form, poisons must be, or must become, either gaseous or liquid before they act; mixture and dilution weaken their activity, though there are exceptions to this rule; and some, which are rather insoluble, such as arsenic, are rendered nearly inert when mixed with insoluble powders of great tenacity, such as charcoal, magnesia, and the like. 3. Chemical changes materially affect their actions; corrosives becoming innocuous by neutralization, purely local irritants being thereby much enfeebled, and all of them being rendered more feeble, or even inert, if they are converted into substances insoluble in the secretions of the textures to which they are applied. Poisons that act through the blood on remote organs are little influenced by chemical changes, except in so far as their solubility is affected; a very important general principle, which ought never to be overlooked in the search for antidotes. Arsenic, mercury, prussic acid, opium, and numberless other poisons, are almost equally active in all their chemical combinations, provided they continue soluble. 4. The effect of the texture acted on in modifying the influence of poisons has been already adverted to. As examples of this, it may be mentioned that prussic acid has little or no effect through the sound skin, nor snake-poison when swallowed; and that strychnia, the active principle of nux-vomica, has no effect through the skin, while one or two grains might prove fatal if swallowed, and a third of a grain would probably kill a man in a few minutes if injected in a state of solution into a wound, into the cavity of the chest, or into a vein. Habit weakens the effects of many poisons, as in the familiar instances of opium and ardent spirits, of which ten or twenty times what is sufficient to prove fatal in ordinary circumstances may be taken with impunity by those who have long used them. Mineral poisons are less under the influence of this modifying circumstance than vegetable poisons; and of the latter those are most influenced which act chiefly upon the brain. It is very difficult to account for the varying effect of habit on the energy of vegetable poisons. Strychnia, for example, the active principle of nux-vomica, seems altogether excluded from the modifying effect of habit; while another principle, analogous in elementary composition and in chemical properties, morphia, the active principle of opium, may through habit be taken without injury in a dose fifteen times as great as what might in ordinary cases prove fatal.

6. Peculiarity of constitution commonly operates in rendering the body more than usually sensible to the action of poisons, as in the case of opium, mercury, and cantharides, medicinal doses of which act with poisonous violence on some. In a few instances original peculiarity deadens the activity of certain poisons, and this is observed still more remarkably during the constitutional state of certain diseases, such as hydrophobia, locked jaw, mania, delirium tremens, and excessive loss of bloods. In some constitutions substances not injurious to mankind generally produce all the phenomena of poisoning. Thus there is scarcely any article of food or drink, except the great staple commodities, beef, mutton, and the simple kinds of bread, which are not at times observed to act poisonsously on some people. But the most remarkable substances of the kind are red fish, shell-fish, mushrooms, bitter almonds in small quantity, and eggs.

It has been stated that poisons are exceedingly numerous, but that they possess only a limited number of actions. As these actions consist of derangement of the functions of certain organs and textures of the body, it follows that the outward signs of these derangements must be circumscribed within certain bounds, and that many poisons must agree with one another in producing the same, or nearly the same, outward signs. This general fact constitutes the basis of the most approved classification. Formerly physiologists endeavoured to arrange poisons according to certain theoretical notions of their nature, or according to certain mysterious properties imputed to them; and subsequently most were content with distributing them in three classes, according to the kingdom of nature whence they happen to be derived. Every classification, however, should have some practical bearing; and as the most important objects in the present instance are the decision of the question of poisoning in a general sense, the discovery of the particular poison, and the treatment of its effects, these points ought to be invariably kept in view. With this understanding, the best classification is obviously that which is founded on the external signs of poisoning, that is, the grouping of the symptoms produced by each. Such is the basis of all the most esteemed modern arrangements.

The whole wonderful multiplicity of poisons, when thus viewed, may be considered as either exciting irritation in particular organs, or disordering the functions of the brain and spinal marrow, or as uniting both these properties. The first are called irritants, the second narcoticos, the third narcoticos-irritants, or more usually narcoticos-acridos. The irritants comprise chiefly the free acids and free alkalis, with many of their compound salts, several earths with their salts, many compounds of the metals, acrid vegetables, and acrid animal substances. These all agree in producing, as their principal phenomenon, destruction or inflammation, sometimes of the part to which they are applied, such as the skin, mouth, throat, intestines, and so forth,—and at other times of organs at a distance from their place of application, such as the stomach, intestines, kidneys, bladder, lungs. And the symptoms they produce are those incidental to inflammation generally, grouped, however, in so peculiar a manner, either in order, kind, or complexity, as in many instances to distinguish the cause which occasions them from any natural cause of inflammation. Many substances arranged among irritants produce effects which would also associate them with the class of narcotics; but still inflammation and irritation are their leading consequences. The narcotics comprise principally opium, prussic acid, the volatile oils of bitter almond, cherry-laurel, and other drupaceous plants; henbane, thorn-apple, deadly nightshade, and certain poisonous gases, such as carbonic acid, carbuncle oxide, carburetted hydrogen, cyanogen, sulphuretted hydrogen. These agree in acting either upon the brain, or upon the spinal marrow, or upon both these parts of the nervous system at once. The symptoms thus arising are stupor and coma, delirium, convulsions, paralysis, with a great variety of less important yet often very significant phenomena. When coma is the chief result, the brain is considered to be chiefly acted on; when convulsions or paralysis occur without stupor or coma, the spinal marrow must alone suffer; and where both sets of phenomena present themselves, it is probable that the whole nervous system partakes more or less of the injury. The narcoticos-acridos comprehend hemlock and other deleterious plants of the family Umbelliferae, black and white hellebore, meadow-saffron, fox-glove, ipecacuan, nux-vomica, coelcus indicus, camphor, poisonous fungi, and all ethereal and alcoholic fluids, besides many others of less note, or not so familiar. It is difficult sometimes to separate the individuals of this class from the narcotics on the one hand and the irritants on the other. But for the most part they produce in different circumstances either narcotism or inflammation alone, or both conjunctly, and that either simultaneously or in succession.

It may be well to illustrate these statements by a brief sketch of the effects of a few familiar or interesting species belonging to each class.

The purest examples of irritant poisons are the strong mineral acids and alkalis, namely, sulphuric, nitric, and muriatic acids, and potash and soda. These, when applied to the external parts of the body for a sufficient length of time, cause corrosion and consequent destruction; and life may be thus brought into imminent danger, either from the extent of the injury and the consequent sympathetic derangement of the vital functions, or from a variety of less direct or incidental disorders. Of such a course of things the public in this country have lately had too many illustrations, resulting from the execrable crime of throwing sulphuric acid over the person. When swallowed, the strong mineral acids and alkalis sometimes act in a great measure on the throat and gullet, more frequently on the stomach and intestines. In the former case there is instant and horrible sense of burning in the mouth, throat, and neck, cruciation of acid matter, often bloody, or mixed with dark masses, excessive tenderness of the injured parts, incapability of swallowing, difficult, husky breathing; and the sufferer may either die suffocated, or from the depressing sympathetic impression produced on the heart; or he may survive for a length of time, perishing, however, miserably in the end, from stricture of the gullet and starvation, or he may recover after the discharge of more or less of the lining membrane of the throat, and a tedious and precarious convalescence. Where the stomach and intestines are acted on by the acids or alkalis, there is in general violent vomiting, often of blood, and, especially after swallowing anything burning pain in the pit of the stomach, extending over the belly, with excessive tenderness and eventually swelling, frequently profuse purging and gripes, and extraordinary prostration of the pulse and of the strength; and the issue may be either recovery, more or less prompt, or far more generally death, at times from the sympathetic depression of the heart and general system, more rarely from gradual exhaustion, occasioned partly by constant irritation, partly by inanition, on account of extensive injury of the internal membrane of the stomach,—on which digestion, probably, in a great measure depends for its integrity. These phenomena are purely the results of local corrosion and irritation. No remote phenomena arise except exhaustion of the heart, from sympathy with the local injury; in particular, there is no disturbance of the function of the brain, spine, or nerves, except what arises simply from exhaustion of the circulation. The most remarkable of all the irritants for subtlety and variety of action conjoined is arsenic. It is not, however, an absolutely pure irritant; for, though irritation of a multifarious nature is its most prominent result, it also disturbs the functions of the nervous system. When applied for some time to the surface of the body, denuded of the scarf-skin, it kills the part to some depth; at least a portion is thrown off by the process of sloughing, showing either that the part had been killed, or that inflammation is produced, of a kind which leads to its death. Both in this manner, and with much greater certainty if it is applied to a fresh wound, or introduced into any of the external openings of the body, or injected in solution into the cavity of the chest or belly, it excites irritation and inflammation, not merely where it touches, but likewise in various distant organs. The stomach and intestines suffer the most invariably, giving rise to violent vomiting, especially of all articles swallowed, burning pain in the bowels, tenderness, griping, purging, and excoriation of the anus. The kidneys, bladder, and organs of generation, are also often affected, causing strangury, suppression of urine, pains in the loins, tenderness in the lower belly, &c. The lining membrane of the air-passages likewise frequently partakes in the injury, as is indicated by hoarseness, cough, difficult breathing, expectoration, and deep-seated pain in the chest. Not unfrequently the investing membrane of the nostrils and mouth presents signs of derangement, such as redness, aphtha, and constant discharge. These symptoms are also generally attended with extraordinary depression of the action of the heart, which is the most frequent cause of death; and this sometimes forms the only prominent effect, the sufferer dying in a few hours, with scarcely any other symptom but mortal faintness. Recovery may take place even though the complicated effects which have been described may have been developed. But after these primary disorders have disappeared, there are important secondary risks to be encountered, such as dropsy, gradual emaciation from constant disturbance of digestion, and, above all, epilepsy, palsy, and other affections characteristic of an action upon the nervous system. Of the symptoms thus indicating a narcotic action, the most pointed and most remarkable are epileptic convulsions and local partial palsy.

To these illustrations of the phenomena of internal poisoning produced by the irritants, it may be well to add a short sketch of the very striking effects produced by many of them as external poisons, when they have been introduced into the substance of the skin or its subjacent cellular tissue, through a wound. Of poisons of the kind now alluded to the most familiar are snake-poison, and the fluids of the dead human body after certain diseases or in some peculiar unknown state; but similar effects are also produced by many acrid vegetables. The affection produced is diffuse inflammation of the cellular tissue, so called because it diffuses itself rapidly along that texture, without any tendency to become circumscribed, as in ordinary inflammation similarly seated. It is attended with some puffy elevation and tenderness of the skin over the inflamed part, but not always with redness—with pain, not always acute, usually of that kind called burning pain—and with excessive depression of the action of the heart; and death may ensue either in a few hours from the derangement of the function of the heart, or more slowly from extensive injury of the cellular tissue, which terminates in gangrene.

Of the phenomena produced by the narcotics, the purest and most familiar example is to be found in the effects of opium. This drug produces a great variety of interesting nervous phenomena when taken in small medicinal doses. When taken in a poisonous dose, it first occasions languor, giddiness, weakness, and drowsiness, afterwards deep sleep, attended in general with complete repose, soft, slow breathing, and highly contracted pupils, and then profound coma, or insensibility, which cannot be dispelled by any stimulants, and which usually proves fatal if it be permitted to be fully formed. In particular cases these symptoms are varied with delirium in the early stage, and convulsions in the advanced stage; but such deviations from the ordinary rule are rare. Belladonna, or deadly nightshade, is another narcotic which produces effects somewhat different. Its berries, which are sometimes eaten by mistake by children and other ignorant people, although they have a mawkish and by no means seductive taste, occasion in the first instance a singular state of very active delirium, in which the individual performs a series of incoherent and extravagant acts with much vivacity, or falls into the condition of somnambulism; and after some hours this is succeeded by a state of deep sopor or coma, as from opium, though more frequently intermingled with convulsions than in the case of that drug. Death is sometimes the result, and would be more frequent were it not that the precurory stage of active delirium often leads to the discovery of the offending cause, and its removal by fit treatment. Prussic acid, another pure narcotic, which is now almost as familiar as opium among poisons, rivals them all in subtlety and rapidity of action. Small animals, such as rabbits, have been killed with it in the brief space of four seconds. A single drop has killed a cat in half a minute, and one grain, or about four drops, has repeatedly proved fatal to man within three quarters of an hour. These statements apply to the pure acid, which is seldom seen; but the common acid of the shops, which is used in medicine, is equally energetic in larger doses; and so are the distilled waters and essential oils of the bitter almond, peach-kernels, cherry-laurel leaves, rowan-tree root, and apple-seeds, which all owe their poisonous qualities to the same cause. The effects produced by all these poisons are immediate, dreadful alarm, giddiness, and hurried breathing, speedily followed by convulsions, insensibility, one or two fits of deep convulsive respiration, and death. The narcotic gases act very much in the same manner with opium, as is well exemplified by the fumes of burning charcoal, and other forms of carbonic acid. When in a pure or concentrated state, carbonic acid extinguishes life immediately, in part by suffocation, on account of the exclusion of respirable air, and partly by its narcotic operation. But when breathed in a diluted state, as in an ill-ventilated mine, or in a confined chamber heated by charcoal, it induces giddiness, fulness of the features, ringing in the ears, gradually increasing stupor, and at length profound insensibility, commonly attended with lividity of the face, glistering of the eyes, and occasional convulsions, which often prove fatal, and always if not speedily relieved by fresh air and other suitable treatment.

The narcotic-acids may be exemplified by a great variety of well-known and powerful poisons. Hemlock, which is believed to have been a familiar poison for more than two thousand years, but whose effects are very generally misunderstood, ought scarcely to be arranged in this class, where it is commonly placed. Its irritant properties are very ill defined. But it is a powerful and very remarkable narcotic, and its active principle, named conva, is scarcely inferior to prussic acid in celerity of operation, or in the smallness of its dose. It seems to act by paralyzing the muscles of voluntary motion and of respiration, without affecting the brain; and the symptoms are weakness of the limbs, gradually pervading the rest of the body, and terminating in loss of the power of motion, while at the same time the respiration, at first laborious, gradually becomes more and more circumscribed and slower, till at length it ceases, the heart all the while acting vigorously, and the sensation continuing unaffected. A better instance of a narcotico-acrid poison is *nux vomica*, and its principle *strychnia*. These are counterparts in action to hemlock and conia. They powerfully stimulate the spinal marrow, producing violent convulsions, like those which attend locked jaw or tetanus, and without impairing the sensibility. The first symptoms are restlessness, undefinable uneasiness, and alarm, speedily followed by fits of stiffness of the jaw and neck, and then by violent paroxysms of muscular contraction, in which the limbs and arms are extended, the features hideously distorted, and the head, body, and legs bent backward forcibly; and the third or fourth fit commonly proves fatal. Strychnia, the source of these dreadful effects, is on a par with prussic acid and conia in energy; for a third of a grain will kill a wild boar in ten minutes, and one grain properly administered would certainly kill a man in half that time. So far this genus of poisons acts like the narcotics; but, in frequent instances, where the narcotic symptoms pass away, they are succeeded by the signs of inflammation in the stomach and intestines, namely, pain, vomiting, purging, and swelling of the belly, which affection, too, may prove fatal. Such irritant effects, however, are rare, perhaps because in the great majority of cases, death is brought about in the early stage by narcotism. A better example still of a narcotico-acrid is *fox-gloves*. A most valuable and safe medicine in small doses, this plant nevertheless acts as a very dangerous poison in large doses; and it sometimes produces in the same case both deep coma with convulsions, and likewise profuse diarrhea, with torrima and tenderness of the abdomen, while at the same time it occasions suppression of urine, and extreme depression of the action of the heart. By far the most characteristic illustrations, however, of the narcotico-acrid poisons are to be found in the *deleterious fungi*, or poisonous mushrooms as they are sometimes called. These differ from most other poisons in their effects being often put off (though to this rule exceptions exist) for several hours, apparently because time must be allowed for the digestion of substances on the whole difficult of digestion. The effects are singularly various; for it has been often observed, that among a number of persons who have partaken of the same poisonous stew, some had only giddiness, confusion, delirium, stupor, coma, and convulsions; while others suffered only from vomiting and purging, distension of the belly, tenderness, and griping; and a third party were seized at first with the former class of symptoms, and on these passing partially off, were attacked severely with the latter.

Besides the irritant, narcotic, and narcotico-acrid poisons, some writers on the subject admit a fourth class, under the name of *Morbid poisons*, comprising those poisonous secretions which are engendered in the body by disease, and possess the property of reproducing by contact or inoculation the same disease to which they owed their own production. The most important of these are hydrophobia, the venereal disease, small-pox, and cow-pox. Authors on toxicology, however, whether physiological or practical, have generally agreed of late in discarding these from the toxicological system, and in arranging the phenomena of their action where they are more philosophically placed, namely, among natural diseases.

In a work like the present, it is not easy to decide how much ought to be introduced of a subject so comprehensive as toxicology, or the science of poisons. The sketch given above will convey some idea of the objects of which it treats, more especially as a branch of physiology. Farther details on the subject at large seem uncalculated for. But there are two departments which may be enlarged on with some advantage, namely, the Evidence of poisoning, and the Treatment of the effects of poisons. Poisoning, both criminal and accidental, has become so common and so notorious in recent times, that there are probably few persons who have not turned their thoughts to these two branches of the subject; and it is desirable for many reasons that correct views should be entertained of them, even by unprofessional persons,—more correct views, at least, than what generally prevail.

Till a very recent date, most erroneous notions were entertained, alike by the vulgar as by scientific men, of the evidence of poisoning. Proofs of the most unsubstantial kind were considered infallible tests of death by poison; and, under the authority of grievous professional error, we now know that courts of law must have sanctioned many a judicial murder. It is not uninteresting to trace these dogmas of antiquity, abandoned as they now are by the scientific, still obstinately adhered to by the unprofessional world as articles of popular belief; and leading, as of old, to constant blunders, which it is now the business and glory of the toxicologist to check, whilst it was formerly his fate to foster and give effect to them.

The evidence of poisoning cannot be thoroughly understood in all its bearings, without a minute knowledge of the multifarious phenomena produced by all ordinary poisons; and, in judicial cases, it is in the end viewed commonly in reference to the supposed administration of a particular substance. It would be out of place to attempt embracing this wide field here. All which can be ventured on is a view of the evidence of poisoning in a general sense, that is, without reference to any special poison,—a topic of great interest in relation to the first suspicions and earliest investigation of supposed cases of poisoning, whether criminal or accidental. The evidence of poisoning in this comprehensive sense is derived from symptoms, from appearances in the dead body, from experiments on animals, from certain moral circumstances, and from chemical analysis.

1. The symptoms are naturally the first particulars to attract attention and excite suspicion. They were once thought adequate to decide singly any question of poisoning. Now we know that natural diseases imitate so closely the phenomena of poisoning, that the symptoms will rarely yield more than presumptive, and only in rare and very peculiar circumstances, absolute evidence. There is nothing in the kind of symptoms taken generally which will distinguish poisoning from certain natural diseases. The natural diseases, indeed, which imitate the effects of one great class of poisons, namely, the irritants, are on the whole rare; yet they are scarcely less a source of fallacy, at least in judicial cases, where certainty, or something like it, must be aimed at. But there are a number of collateral circumstances connected with the symptoms, which, if taken together, will often supply a very powerful criterion in supposed cases. Thus, in the instance of by far the greater number of poisons, and of almost all which are used for a homicidal or suicidal purpose, the symptoms begin soon after food, drink, or medicine has been taken, commonly within an hour, often much sooner; and in respect of not a few common poisons, such as the mineral acids, mineral alkalis, hartshorn, prussic acid, oxalic acid, they must commence immediately. In general, too, the symptoms begin suddenly, advance quickly, and prove speedily fatal. For the most part they are steady in their progress, exclusive of the influence of treatment. They are upon the whole uniform in their nature. And they appear in the great majority of cases abruptly during a state of good health. The consideration of these characters will not unfrequently en- able the man of experience to pronounce that suspicions which have prevailed of poisoning are wholly unfounded; but, taken singly, they will never justify, on the other hand, more than a presumption in favour of poisoning. It must at the same time be observed, that when these general characters are all applicable, and concur with a certain complicated grouping of the symptoms in particular cases, the presumption becomes very strong; and when other articles of general evidence are added, the proof may be all but complete, nay, absolutely so. Such is clearly the state of the case in not a few instances of poisoning with the mineral acids and alkalis, with arsenic, corrosive sublimate, nux-vomica, oxalic acid, prussic acid, alcoholic fluids. 2. The same confident reliance was long placed in the appearances of the body after death, as in the symptoms, and with even less reason. The discovery of certain morbid appearances may prove poisoning to have been impossible; and yet even here an opinion should not be formed without reserve, because the discovery of the effects of natural disease in the body, even in an advanced stage, is no absolute proof of death from that disease. Poison, as in many authentic cases, may have been nevertheless administered, and have proved the real occasion of death. But there is never anything in the appearances after death which will bear out a general charge of poisoning, as was once universally thought. It should be particularly known, that the vulgar prejudice, which discovers poison wherever the skin becomes unusually livid after death, or wherever the body undergoes prompt decomposition, is utterly without support from scientific experience. Nay, in regard to the latter character, evidence has been proved in recent times to be deducible from the very opposite condition, or the unusual preservation of the body from decay, which is now well known to occur in many cases of poisoning with arsenic. There are certain morbid appearances in the dead body, especially upon the skin, and in the throat, gullet, and stomach, which will furnish the strongest presumption, nay, according to good authorities, almost absolute proof, of poisoning with certain substances, for example the mineral acids; but the details cannot be entered upon here, because a full enumeration, and much professional skill, are required for appreciating precisely their import. 3. Experiments on domestic animals, made with suspected articles, were once supposed to furnish the best of all evidence; and this was probably the best evidence to be had in the days when chemistry and chemical analysis were all but unknown. Now, however, such experiments are not admitted, either by medical or legal authorities, to be of any weight, except under particular circumstances. They are admissible, and indeed clearly indispensable, for deciding questions in toxicological physiology which may arise during trials. They ought also to be allowed some weight when they have been observed accidentally, as, for example, when the remains of suspected articles have been devoured incidentally by domestic animals, especially by a number of them, and above all by the dog or cat, with the effect of producing in them symptoms and appearances after death similar to what were witnessed in the suspected case in the human subject. The objection drawn against such evidence, that the effects of many poisons on the brute creation are different from their effects on man, though fundamentally sound, has been allowed to operate far too sweepingly in modern times. The differences in respect to many common poisons are by no means so great as was thought not very long ago; and upon two animals, the dog and the cat, the effects of most poisons are almost identical with those observed in man, due attention being paid to differences in dose, and to the singular facility with which these animals discharge poisons by powerful early vomiting. But the objection here stated may be allowed sufficient force to put an end to experiments made expressly on animals with suspected articles.

There is, however, a more urgent objection to such experiments,—that they involve the consumption for doubtful evidence of the materials from which decisive evidence may be obtained by other means; for if there is poison enough left to affect sensibly the lower animals, there is amply sufficient for detection by chemical analysis. Accordingly, express experiments with remains of suspected food, drink, or medicine, are now abandoned by all good authorities in toxicology. 4. There are certain moral circumstances which may also be often taken into account in the evidence of poisoning in a general sense, when viewed as a scientific question, because they cannot be correctly appreciated except by a scientific man, and consequently they belong in some measure to the scientific or toxicological proof. The chief particulars are as follows. It may be proved that poison has been purchased, of a kind which may produce the symptoms observed. A suspicious article may be proved to have been administered, either from its taste, or from its having been recommended for properties either absurd in nature, or such as the pretended article is not thought even by unprofessional people to possess, or from a comparative analysis of the materials for making the suspected article, showing that something injurious must have been added at a particular time, and by a particular person. It may be proved that exacerbations of the symptoms have repeatedly occurred soon after articles were given in a suspicious manner. It may be proved that the person poisoned, or a second party under suspicion, exhibited by words or deeds an intention to administer poison, as by assigning impossible properties to what is administered, or by manifestly changing medicine which has been prescribed. A highly important circumstance is the simultaneous and similar illness of several individuals who have partaken of the same meal, coupled perhaps with the degree of their illnesses concurring with their respective shares, and probably also united with the escape of others of the same company who did not partake of the meal, or of particular dishes or liquors. Many other moral circumstances might be here alluded to, by which the question of poisoning in a general sense may be often materially cleared; but as they do not belong to the scientific view of the question, either directly or indirectly, they may be passed over. 5. The chemical evidence is justly considered the best of all the departments of proof; for it not only establishes poisoning in a general sense, but likewise points out the particular poison. There is no department of toxicology which has made such amazing progress in recent times as that of toxicological analysis. A century ago, the search for the remains of poison in suspected dishes, or in the dead body, was scarcely ever attempted, and, owing to the ignorance of the chemical properties of poisons, could not have been successful. Even no more than five-and-twenty years ago, the method of analysis was in all cases crude and unsatisfactory, and for many poisons good processes continued unknown; so that it was no uncommon thing for charges of poisoning to break down, solely on account of the dubious quality of the chemical evidence. But at present, the proof of poisoning is scarcely ever defective in the chemical branch; the evidence of death by poison is usually complete; and how can it fail to be so in competent hands, when the chemist can detect in the most complex mixtures the minute quantity of a twentieth or fiftieth of a grain of the common poisons, and when many years of interment frequently cannot withdraw the crime of the poisoner from the keenness of his search? It has been proved by careful experiments, that the mineral acids, arsenic, corrosive sublimate, blue vitriol, opium and its principle morphia, strychnia the principle of nux-vomica, cantharides, and other less familiar substances, may be discovered in the body of animals poisoned with them, though buried for nine months; and instances have occurred of the detection of arsenic in man Poison.

after interment for two, four, and even seven years. It does not absolutely follow that death has been occasioned by poison because poison is found within the body after death; for it may have been feloniously introduced afterwards, for the purpose of falsely imputing poison; or, though poison has been swallowed, death may nevertheless have arisen either from natural disease, or some other kind of violence. Instances of such extraordinary occurrences are absolutely not uncommon, sufficiently so at least to require being kept always in view. The determination of them involves too refined an inquiry to be considered here. On the other hand, the non-discovery of poison after death is still farther from being evidence that death was not occasioned by poison. For many poisons are still undiscoverable by any method of analysis; others are soon decomposed within the body after death, such as prussic acid; others are quickly absorbed from the stomach during life, so as to prove fatal without leaving any remains behind, as in many instances of poisoning with opium; others may be expelled by vomiting, and nevertheless have, in the first instance, occasioned injury enough to prove fatal, as sometimes happens in the case of arsenic, and very commonly in poisoning with mineral acids. It has, however, been made a subject of question, whether the evidence of poisoning can ever be considered as complete, so as to involve a conviction in a criminal case, unless poison be found either in the body or in the remains of a suspected article which has been swallowed. It appears absurd, however, to insist on the absolute necessity of such evidence. For were the poisoner to choose his means skilfully, and avoid over-doses, he would, on such principles, almost constantly escape. And the best scientific authorities, in the most recent times, seem inclined to allow that the general evidence, from the various sources detailed above, may be often so strong as to leave scarcely any scientific doubt of the occurrence of poisoning; and the conjunction of the circumstances of ordinary evidence may, in a legal sense, entirely remove what little doubt may have existed of a scientific nature. Accordingly there have been instances of condemnation lately in this and other countries, where poison could not be discovered. It may be right to add, that it is most singular how effectually and how quickly poisons are sometimes removed beyond the reach of analysis by incidental causes, even those poisons which may be detected in other circumstances in extremely minute quantities, and where the methods of analysis are well understood. Prussic acid is seldom to be detected if life be prolonged for half an hour, while in the ordinary cases of death in a few minutes it may be discovered with ease. Arsenic, which in the great majority of cases adheres obstinately to the stomach, and may in consequence be detected there though life has been prolonged under frequent vomiting for two days and upwards, has been known to be removed beyond the reach of analysis in the short space of five hours.

Treatment. The treatment of poisoning, like all other branches of toxicology, has, within a few years, been prodigiously improved. It may be said, indeed, to have been understood only within the last quarter of a century. In ancient times the notions entertained of the treatment were not less crude than those formed of the nature and action of poisons. Among other errors, it was strangely supposed that certain counter-poisons existed, which not only possessed the property of curing the effects of all poisons indifferently, but which likewise, when taken for a length of time, had the faculty of impregnating the constitution, and rendering it proof against the influence of any poison. Princes and others often lived thus for years under the care of their physicians, or protected against their treachery, by being charged with conservative antidotes. After these notions were exploded, other erroneous practices came into vogue; and, in particular, it was believed to be established on the basis of observation, that certain antidotes, such as vinegar, milk, oils, and the like, which are really not amiss in some forms of poisoning, were equally efficacious in all. These illusions have been dispelled, even among professional people, only within a very few years; and among the unprofessional they still have currency. The clearing away of the mists of error has been attended with the discovery of many real and most valuable remedies. The improvement which has taken place has been owing partly to the improvements made in chemistry; but in this way nothing could have been ultimately effected without the aid of physiological experiment, and more especially of experiments on animals, a method of inquiry, nevertheless, which it has been too much the practice of an ignorant or spurious humanity to decry.

The treatment of poisoning is directed to three objects, the removal of the poison, the administration of an antidote, and the cure of the disorders which have been produced.

1. The first object, in every instance, is the prompt removal of what may remain of the poison. If it had been applied outwardly to a sore or wound, it must be carefully wiped or washed away. When introduced deep into or under the skin by a puncture, it is to be withdrawn by suction with the mouth, and, still better, with a cupping-glass, the efficacy of which is insured, as in the case of snake-poison, by a bandage being applied above the wound, so as to obstruct the return of blood from the veins to the heart, but without compressing the arteries. Another plan, which has been found effectual in the like circumstances, is simply to apply the bandage above the wound, and then to open a vein between the wound and bandage, so that the poison is drawn from the wound with the blood, and discharged outwardly from the orifice in the vein. Sometimes it is useful to make deep scarifications before applying the cupping-glass; yet in this way the bottom of the wound may be missed; and, on the whole, if incisions are to be made at all, it seems better to calculate the probable depth of the wound, and to remove a portion of the texture with the knife all around it. The bleeding which follows commonly effects the discharge of the remaining poison; but some afterwards add the use of an incandescent iron for cauterizing the whole adjacent parts. The removal of the poison, when taken internally, may be variously managed. But, first, care must be taken not to attempt its removal when nature may have already looked after this step in the treatment, as in the case of profuse, and frequent, and full vomiting. All that is necessary in such circumstances, is to give occasional draughts of lukewarm water, or milk and water, to render vomiting easy, and to aid in washing out the stomach. When vomiting does not occur, or is not free, an emetic ought to be promptly given. Whatever is nearest should be first tried, mustard, for example; but the most effectual is white vitriol, in the quantity of a scruple or half a drachm, dissolved in a large wine-glass-full of water, to be repeated in fifteen minutes if necessary. Where the symptoms indicate narcotic poisoning,—for instance, with opium,—it is essential to keep the person roused after giving the emetic; otherwise it will hardly act. Emetics, when they do operate, are greatly preferable to the stomach-pump, which has been of late currently substituted for them. The stomach-pump, however, is one of the most important additions which have been made to the healing art in modern times. In very many instances of narcotic poisoning no emetics will operate; and all such cases, till of late, inevitably perished where the quantity of poison was considerable. The stomach-pump insures the prompt removal of almost all poisons; so that when used in time recovery is next to certain, where formerly a large majority of cases proved fatal. 2. By all such means, however, the poison is often but partially removed. Some of it pervades the system; more of it impregnates the tissues with which it was in contact, and is ready for absorption; much of it often passes down into the intestines; occasionally it adheres with obstinacy to the inner membrane of the stomach, and cannot be dislodged either by emetics or by washing through means of the stomach-pump. The second object, then, is to administer an antidote. Antidotes have usually been conceived to be of two kinds. Some, by changing the chemical form of poisons, render them inert, and are called chemical antidotes. Others are thought to subdue the morbid action of poisons by exciting a counter-action, and are termed constitutional antidotes. In ancient times, and likewise until the recent improvements in toxicology, scarcely any other antidotes were known, except what belonged to the constitutional class. But it is now thought that in correct language scarcely any such antidote exists. European physiologists are not acquainted with any decided constitutional antidote for any of the numberless multitude and variety of poisons now familiar to the scientific. It is very generally believed, however, that savages in all quarters of the world are in possession of remedies of this nature, more especially for the effects of snake-poison. Apparently authentic accounts have been published, of a considerable variety of antidotes known to the natives in different parts of North and South America for the bite of venomous snakes. But none of these supposed antidotes have been found to stand the test of scientific investigation; natives who put trust in them have been seen to perish in the usual way; there is no difficulty in accounting for their apparent occasional success; and those who give faith to the marvels of travellers on the subject ought to consider how very extraordinary it would be, if, in every part of the globe where there are savages, discoveries of this kind should be made in regard to their poisons, while, with all the advantages of science to aid them in the search, no civilized people have yet contrived to stumble on a similar discovery in relation to any of the innumerable poisons with which they have long been familiar. If constitutional antidotes are still much wanted, there is no want of excellent antidotes of the chemical class. Some of these act by neutralizing the chemical qualities on which the properties of the poison depend, others by simply rendering the poison insoluble. Thus sulphuric acid is rendered inert by magnesia, because it becomes thereby a neutral salt, soluble, indeed, but no longer capable of corroding the animal textures, or of exciting violent irritation. In like manner potash is rendered inert, or nearly so, by lemon-juice or vinegar, or, though less easily, by oil, because it is converted into neutral salts, which are feebly irritant and not at all corrosive. On the other hand, oxalic acid is rendered inert by magnesia, partly because its corrosive qualities are neutralized by chemical neutralization, but chiefly because these, in common with its not less formidable effects on the nervous system through absorption, are prevented by a substance resulting which is insoluble. So, too, arsenic becomes inert when brought thoroughly in contact with the hydrated peroxide of iron, because an insoluble compound is formed, the arseniate of iron. In using and searching for antidotes of the chemical kind, several important general rules should be attended to. For, first, where a poison is a pure local irritant, destitute of action through the blood or remote organs, it is usually sufficient that it be neutralized; because the resulting compound is commonly but a feeble irritant, although soluble. One condition, however, must be observed, namely, that the antidote shall be itself innocuous, otherwise harm may be done by the antidote before it comes in contact with the poison, or because it is given in excess. Thus the mineral acids are unfit antidotes for neutralizing the mineral alkalis, and the latter for neutralizing the former. But, secondly, when the poison is of a kind which acts on remote organs through the medium of absorption, it is not enough that it be chemically neutralized. For all such poisons act as such throughout their soluble compounds; their compounds act on the whole in proportion to their solubility; and those only are inert which are insoluble, and insoluble not merely in water, but likewise in the animal fluids of the stomach. Hence oxalic acid and arsenious acid (common arsenic) are not neutralized in their physiological actions by being neutralized with potash; prussic acid similarly treated remains as energetic as ever; and the powerful vegetable alkaloids, morphia, strychnia, conia, and the like, instead of becoming inert by neutralization with acids, are rendered positively more active, because they are made more soluble. In the case of every poison, then, it is advantageous, and in very many it is indispensable, that the chemical change effected shall be such as to impart to the compound insolubility; and care should be taken that this insolubility shall exist in regard to the natural juices of the stomach, which are commonly acidulous. But, thirdly, the antidotal tendency of such chemical remedies, even when of undoubted virtue, is often counteracted where the poison is a fine rather insoluble powder; for it adheres forcibly to the inner coat of the stomach, irritates it to throw out tough mucus, which covers the powder, and defends it against the approach of the neutralizing agent. Frequent instances of such a course of things occur in the case of poisoning with arsenic. 3. The last object of the treatment of poisoning is the cure of the disorders which the poison has produced. These disorders, since they are substantially natural diseases, must be treated as such. But there are certain circumstances which render them in some measure peculiar, and consequently modify the treatment. These are chiefly as follows. Treatment will obviously be of little use for such disorders, until what remains of the poison be removed or rendered inert; and as this object is often unattainable, ultimate success is frequently beyond reach. Evacuation of the poison is in this point of view of primary importance, as well as for its own sake. In the case of poisoning with the irritants, the treatment is often exceedingly embarrassing, because it must be simultaneously directed towards two opposite ends, the suppression of inflammation by evacuating, and consequently debilitating measures, and the removal of depression of the heart and general system by stimulating remedies. These two contrary and incompatible objects are often the cause why the best treatment proves inefficacious. The treatment of narcotic poisoning is somewhat differently circumstanced. The remains of the poison being removed, there is only the induced disorder to combat. These disorders are in the great majority of cases functional only; that is, no structural injury has been occasioned. Hence, the offending cause having been withdrawn, there may be expected to prevail in the constitution a natural tendency to throw off the functional disorder,—a tendency towards recovery. Experience shows that such is actually the fact. If in narcotic poisoning the remains of the poison can be removed, and life can be preserved for a moderate length of time, success is highly probable in a great majority of cases. Thus very few die of poisoning with opium, and perhaps still fewer ought to die in skilful hands, who survive for eighteen hours. In narcotic poisoning, then, the treatment for subduing the disorders induced consists mainly in employing, in some instances, sedatives for subduing irritation of the nervous system, but much more commonly stimulants, for the purpose of keeping the person roused, and in applying various means for supporting artificial respiration where the natural breathing fails. Excellent methods for accomplishing the first object are now in familiar use, such as loud talking, agitation of the body, injecting water into the ears, tickling the nostrils, dashing cold water over the head and shoulders, applying snapsms to the calves, blistering the head with boiling water, and internally ammonia, ether, and spirits. But the best method of supporting artificial respiration has not yet been discovered; there are practical objections to all the methods yet devised; and it is only when these shall be perfected, that the treatment of narcotic poisoning will be rendered substantially superior to what it is at present. It is not unlikely that galvanism will be found a material part of the most efficacious method,—applied, however, not continuously, as is often practised, but interruptedly, so as not to disturb the alternate contractions and relaxations of the respiratory muscles.

In the preceding observations on the effects and treatment of poisoning, poisons have been regarded solely in their operation on the animal body. But they were defined at the outset as acting on living bodies generally; and upon vegetables their action is not less remarkable than upon animals. This branch of the subject has been hitherto little studied; but what is already known of it seems full of interest both in a physiological and in a practical point of view. It appears that in a general sense there is a close analogy between the actions exerted by poisons on both divisions of the living world. As there are two leading effects produced in animals, so are there two great classes of phenomena developed in vegetables, those of irritation and those of narcotism, or at least of an action closely analogous. The apparent phenomena of both kinds are indeed much simpler in vegetable than in animal beings, partly because the organs and functions of the former are more simple than those of the latter, partly because physiologists have not yet ascertained with precision the special changes that are induced. Still, however, it is easy to trace in vegetables the leading effects produced by irritants and by narcotics respectively, upon animals. The former occasion partial or general disorganization or death of the organs of plants to which they are directly applied, and the plant may eventually either recover or perish, according to the extent of the injury or the importance of the organ injured. The latter seem to act upon the vitality of the plant, without in general producing any marked change of a local nature, or such as may be referred to a direct impression, at least until the first signs of vital depression appear; and it is commonly observed, that so soon as such signs of depression do make their appearance, however slight they may be, they quickly pervade the whole plant, which in consequence perishes irrevocably. The irritants appear to act topically, and from without inwards; the narcotics act more generally, and from within outwards, being probably first absorbed.

Poisons act upon vegetables, through whatever channel they are introduced, and to whatever organ they are applied, provided the texture be such as to admit of their passage to those parts which are more or less directly connected with life. The organs through which they act with greatest energy are the leaves and the roots. Liquid poisons act with most energy through the roots; gaseous poisons are probably most energetic when applied to the leaves. Partial action is sometimes produced by the topical application of a general or narcotic poison; thus arsenic introduced into the axilla of a leaf of the *dipsacus fullo* kills the whole superior part of the plant on the side corresponding with the leaf. Vegetable poisons are not less energetic than mineral poisons. Nay, however extraordinary it may appear, there seems no question that plants may be promptly killed by their own poisons,—that the poison produced by a particular species may kill that species as readily as it will others, if applied to the root so as to be absorbed into the nutritive juices. This singular phenomenon may depend on the poison being secreted and confined in particular receptacles in the ordinary state of the plant. But another and more intelligible explanation in regard to certain poisons may be drawn from the well-ascertained fact, that some vegetable poisons, and probably more of them than the physiologist may at present be inclined to admit, do not exist ready formed in the plants whence they are obtained, but are produced only when certain principles, existing naturally apart in distinct receptacles, are brought into contact by mechanical force or chemical manipulations. A remarkable instance in point is the essential oil of the bitter-almond kernel, or cherry-laurel leaf, which does not exist ready formed, otherwise it would be betrayed, like other essential oils, by its powerful odour, but is formed only when certain principles, named *amylodalin* and *emulsion*, are brought in contact with each other and with water.

No poisons are better fitted for illustrating the phenomena of poisoning in vegetables, or better deserve the attention of physiologists and practical men, than those which are gaseous in their nature. Most of them seem to act in excessively minute quantities and proportions. A tenth part of a cubic inch of muriatic acid gas, which is equivalent to the twenty-fifth part of a grain by weight, will in no long time destroy a small plant, although the gas be diluted with twenty thousand times its volume of air; and the devastating effects produced on surrounding vegetation by all manufactories where this acid is thrown abundantly into the atmosphere, as in the manufacture of black-ash and soda from sea-salt, abundantly show that far less proportions will prove equally deleterious when applied continuously. Sulphurous acid gas acts with nearly as great intensity. The effect of either of these poisons is simply to shrivel and wither the leaves and buds, like the action of frost in spring; and the plant will eventually recover if removed in time from the influence of the noxious agent, but with the loss of its foliage. Other gases, such as sulphured hydrogen and cyanogen, produce no visible change until the leaves begin to bend and droop; after which the drooping quickly extends, till at length the whole plant becomes flaccid, so as to present exactly the same appearance as when deprived of moisture; and it perishes inevitably.

Some substances which are poisonous to animals are not poisonous to vegetables. The experiments which have been made on this subject are neither sufficiently extensive nor sufficiently exact to warrant any general deductions. A very remarkable instance is carbonic acid gas, a small proportion of which in the atmosphere will speedily extinguish animal life, but which is innocuous to vegetables in almost any proportion, nay, on the contrary, is commonly thought to supply them with aliment.