GENERAL PRINCIPLES Definition.-Toxicology is the science that treats of poisons, their origin, properties, and action on the system, the treatment of their noxious effects, and their detection by chemical or other means. Up to comparatively recent years the science of toxicology embraced in its domain only poisons of well-defined character, coming chiefly from the mineral and vegetable kingdoms, such as arsenic, strychnin, and morphin. Within a relatively short time, however, it has been discovered that a large number of diseases are produced by the action of certain poisonous substances generated within the system either by the normal cells of the body or by micro-organisms. These compounds, known according to their origin and properties as leukomains, ptomains, toxins, etc., properly come within the scope of toxicology and give to the science a greatly increased field. It naturally is not customary, however, to deal with these substances in works like the present on forensic toxicology, but rather to leave their discussion to books on pathology and the practice of medicine, or to treatises devoted especially to them. It is a difficult matter to give an exact definition of the term "poison." This arises from the fact that it is impossible to set aside any group of substances that are poisons under all conditions; a body may be entirely harmless under certain circumstances, and yet under others be possessed of dangerously poisonous properties. The salts of potassium, for example, in small quantity are not only not poisonous, but are necessary for the maintenance of a healthy condition of the body; in large doses, however, they are active poisons, capable with great certainty of producing death. Most medicines if administered in too large quantity become poisons; and conversely, nearly, if not quite all, poisons, if given in small doses, are possessed of remedial properties. The line, in fact, between a medicine and a poison is often exceedingly narrow. No substance is known that is a poison in all doses; a certain amount, varying, however, very widely with different bodies, is necessary in order that poisonous effects may follow its administration. The definition given by Taylor is, when slightly modified, perhaps as comprehensive and as scientific as any: A poison is a substance which, when absorbed into the blood, is capable of seriously affecting health or of destroying life, and this as its usual effect upon the healthy body. It will be observed from the above 1 On Poisons, p. 18. First, that a poison is a material substance, and not an imponderable agency, such as electricity or heat. Second, that it is a body which acts after absorption into the blood, and does not produce its effects, therefore, by mere mechanical action. Pounded glass, needles, and other similar articles, although capable of producing death when taken in sufficient quantity, act mechanically only, and are not poisons in the true sense of the word. For similar reasons, it may be a question whether the corrosive acids and alkalis should be considered as poisons. Their chief effect is a local one and is produced without absorption into the blood, and on this account some writers on toxicology do not embrace them under the strict head of poisons. Since, however, in nearly all cases a certain part of the corrosive agent enters the circulation and produces harmful systemic effects, their exclusion from the category of poisons seems on the whole unnecessary, and for many practical reasons undesirable. 1 Third, that a substance which produces noxious effects as an unusual result, or by acting upon a diseased body, is not necessarily a poison. Many ordinary articles of food, as is well known, are occasionally the cause of distressing and sometimes even of serious symptoms when taken by people who have an idiosyncrasy to them. Strawberries cannot be eaten by a considerable number of people without unpleasant effects, and the writer is acquainted with a gentleman in robust health who is made exceedingly ill not only by eating apples, but even by their odor. Strawberries and apples, however, manifestly should not come within the definition of a poison; nor do they, as the term is defined above, as the noxious results noted are not their usual effects. And similarly, improper articles of food, which have more than once produced fatal effects with typhoid patients, are equally excluded by our definition from the category of poisons. Fourth, that whether a substance is a poison or not is in no way dependent on the quantity that must be used to produce noxious results. Half a grain of strychnin may produce death, while sixty grains of oxalic acid are required to occasion fatal results. Although from a strictly scientific standpoint the size of dose necessary to produce noxious effects has nothing to do with the conception of a poison, yet, as commonly understood and as generally accepted in ordinary life, the term "poison" is closely connected with the amount required to induce serious results. Common salt in massive doses is capable of producing noxious effects, and has even occasioned death, but it is not commonly looked upon or spoken of as a poison, the quantity required for these results being so large. We may say, perhaps, in a general way that in the everyday affairs of life a substance to be regarded as poisonous must be capable of inducing 1 Witthaus and Becker, Medical Jurisprudence, Forensic Medicine, and Toxicology, vol. iv., p. 43. 2 Gould and Pyle, Anomalies and Curiosities of Medicine, p. 489, where several cases of illness and one of death from the eating of strawberries are cited. 3 Medical Times, January 4, 1840, p. 133 (referred to in Woodman and Tidy's Forensic Medicine and Toxicology). harmful results if administered in doses of about sixty grains, if a solid, or a teaspoonful if a liquid. This limitation, although somewhat arbitrary, is often of great convenience in the common use of the word "poison" and in the discussion of the subject in medicolegal cases. In order to avoid any uncertainty as to the inclusion of the corrosives and the mechanical irritants, the statutes commonly speak of "the administration of a poison or of other noxious or destructive thing," or use other words to the same effect. Legal quibbling in regard to definitions is thus eliminated or reduced to a minimum. Classification of Poisons.-A large number of classifications of poisons have been suggested, but none of them is entirely satisfactory. Two general systems of classification have usually been adopted, the first depending upon the origin or nature of the substance; the second, upon the effect it produces on the system. Were our knowledge of the actions of poisons absolutely definite, the second system of classification would unquestionably be the most desirable; but since, in the present state of science, our information on this point is by no means complete, any close classification made upon this line is necessarily faulty. A simple, general division of poisons, however, into corrosives, irritants, and neurotics, according as the chief effect produced is local corrosion, gastro-intestinal irritation, or altered action of the nervous system, is often exceedingly useful, and is the one I prefer if the classification is based on the effects shown. In this classification under corrosives are included the strong acids and alkalis, whose most important action is local destruction of the tissues; under irritants, those numerous substances, such as arsenic, antimony, mercury, and most of the other heavy metals, phosphorus, bromin, iodin, and a certain number of organic substances like cantharides, savin, and croton oil, whose most conspicuous effects are usually gastrointestinal irritation, as shown chiefly by vomiting, purging, and local pain; and under neurotics, the majority of organic poisons, prominent among which are alcohol, chloral, chloroform, opium, belladonna, aconite, strychnin, acetanilid, carbon monoxid, hydrocyanic acid, and carbolic acid, all of which expend their toxic powers chiefly on the nervous system, producing delirium, coma, convulsions, and disordered circulation and respiration as prominent symptoms. Even this division, however, is seriously deficient and far from satisfactory, as very many poisons act in two or more different ways : oxalic acid in concentrated solution is a corrosive, in dilute solution an irritant, and in either case it also acts powerfully on the nervous system, and the same may be said of mercuric chlorid, carbolic acid, and numerous other poisons. As an interesting contribution to this system of classification we give below the grouping of poisons suggested by Rabuteau.' It is faulty, as any classification on this line must necessarily be in the present state of our knowledge, but is suggestive of what may finally 1 Eléments de toxicologie, p. 31. |