276 POISONS usually of a specific character, though some writers group the remote effects of poisons under two heads, and speak of the common and the specific remote effects of a poison. The local action of a poison of the corrosive class is usually so well marked and obvious that the fact of the adminis tration of a poison of this class is generally unmistakable. The same may be said, in a less degree, of the irritant poisons, especially the mineral irritants ; but here the symptoms sometimes so closely simulate those of natural d isease as to render the recognition of the administration of poison a matter of difficulty. Hence an accurate acquaint ance with the remote specific effects of the various poisons is indispensable to the medical jurist. The class of poisons which has been administered or taken will thus be sug gested to his mind by the observation of the symptoms ; and not unfrequently the specific poison taken will be suspected. It is almost universally admitted that absorp tion of a poison is necessary for the production of its specific remote effects, and the old notion that a poison may kill, by its action through the nervous system, without absorption, is abandoned. Modifying Circumstances. The ordinary action of a poison may be greatly modified by the largeness of the dose, by the state of aggregation, admixture, or of chemi cal combination of the poison, by the part or membrane to which it is applied, and by the condition of the patient. Thus, for example, opium may be a medicine or a poison according to the dose in which it is given ; and a dose of the drug which may be beneficial to an adult in certain states of the system may be fatal to a child, or to an adult when suffering from some forms of disease. All barium salts, again, are poisonous, except the quite in soluble sulphate. The simple cyanides, and many double cyanides, are highly poisonous ; but yellow prussiate of potash, which is a double cyanide of iron and potassium, is almost without action upon the system. The part or tissue to which a poison is applied greatly affects the activity of a poison, owing to the varying rapidity with which absorption takes place through the cutaneous, mucous, and serous surfaces, and by the other tissues of the body. Curare, an arrow poison, may be swallowed in considerable quantity without appreciable result, whilst a minute quantity of the same substance introduced into a wound is speedily fatal. Idiosyncracy has an important bearing in toxicology. Pork, mutton, certain kinds of fish, more especially shell fish so-called, and mushrooms have each produced all the symptoms of violent irritant poisoning, whilst other persons who have partaken of the same food at the same time have experienced no ill effects. Some persons are stated, on good authority, to be capable of taking with impunity such poisons as opium, corrosive sublimate, or arsenic, in enormous doses, and this irrespective of habit, which is known to have such an influence in modifying the effects of some poisons, notably the narcotics. A tolerance of poisons is sometimes en gendered by disease, so that a poison may fail to pro duce its customary effect. Thus, opium is tolerated in large quantities in tetanus, and in delirium tremens ; and mercurial compounds may in some febrile affections fail to produce the usual constitutional effects of the metal. On the other hand, diseases which impede the elimination of a poison may intensify its effects. The evidence that a poison has been administered is based upon the symptoms produced, on the appearances met with in the body after death, on the analysis of articles of food and drink, of excreta and ejccta, and of the organs of the body after death, and on physiological experiments made with substances extracted from the same articles. These physiological experiments are usually made upon animals, but in some cases, as for instance when aconite has to be searched for, the physiological experiments must be made also upon the human subject. The evidence obtained from one or more of these sources, as compared with the properties or effects of various known poisons, vill enable the medical jurist to form an opinion as to the administration or non-administration of a poison. The symptoms exhibited by the patient during life rarely fail to afford some clue to the poison taken. Persons may, however, be found dead of whose history nothing can be learned. Here post-mortem appearances, chemical analysis, and, it may be, physiological experi ments are all-important for the elucidation of the nature of the case. Poisoning may be acute or chronic. The general condi tions which should arouse a suspicion of acute poisoning are the sudden onset of serious and increasingly alarming O t/ symptoms in a person previously in good health, especially if there be pain in the region of the stomach, or, where there is complete prostration of the vital powers, a cada veric aspect, and speedy death. In all such cases the aid of the analytical chemist must be called in either to con firm well-founded or to rebut ill-founded suspicions. The mode of treatment to be adopted in the case of poisoned persons varies greatly according to the nature of the poison. The first indication, when the poison has been swallowed, is to evacuate the stomach ; and this may usually be done by means of the stomach-pump when the poison is not of the corrosive class ; or the stomach may be gently washed out by means of a funnel and flexible siphon-tube. In many cases emetics are valuable. Anti dotes and counter-poisons may then be given. The former are such substances as chalk to neutralize the mineral acids and oxalic acid ; the latter have a physiological counter action, and are such as atropine, which is a counter-poison to morphia. These may usually be administered most effectively by hypodermic injection. The stomach may to a certain degree be protected from the injurious effects of irritants by the administration of mucilaginous drinks ; alkaloids may be rendered sparingly soluble by means of astringent substances containing tannin ; and pain may be relieved by means of opium, unless contra-indicated by the nature of the poison. The effects of the convulsant poisons, such as strychnine, may be combated by means of the inhalation of chloroform. The classification of poisons is a matter of difficulty. Various attempts have been made to classify them scienti fically, but with no signal success ; and perhaps the best system is that which groups the various poisons according to the more obvious symptoms which they produce. Our knowledge of the more intimate action of poisons is still too imperfect to admit of any useful classification according to the manner in which they specifically affect the vital organs. Poisons may in the manner indicated be classified as (1) Corrosives, (2) Irritants, (3) Neurotics, and (4) Gaseous Poisons. The subject of poisonous food has already been treated under the heading MEDICAL JURIS PRUDENCE (vol. xv. pp. 781-2). 1 . Corrosives. The typical member of this class is corrosive sublimate, the soluble chloride of mercury. In it are included also the concentrated mineral acids (sulphuric, nitric, and hydrochloric) ; oxalic acid ; the alkalies (potash, soda, and ammonia) and their carbonates ; acid, alkaline, and cor rosive salts of the metals (such as bisulphate of potash, alum, butter of antimony, and nitrate of silver) ; also carbolic acid. The symptoms produced by the mineral acids and the alkalies are almost altogether referrible to local action; but
some corrosive poisons, such as carbolic acid, produce,