Immunity.
The modern employment of serums in the treatment of zymotic diseases goes a long way towards explaining the fact of the immunity of individuals in respect to bacterial poisons. But the possibility of immunity against such poisons as arsenic, opium, or serpent venom appears to rest on a different basis. In 1896 Professor (now Sir) Thomas R. Fraser, M.D., F.R.S., reported to the Royal Institution a long investigation dealing with the alleged resistant power of certain tribes or sects in India, Africa, &c., who can suffer the bites of unquestionably venomous snakes without becoming seriously affected. After quoting numerous reports from old and recent works showing that this immunity is an actual fact, Professor Fraser described a long series of experiments extending over many years with venom which he had obtained from India, America, Africa, and Australia. The venom, he stated, is a complex substance and is not a ferment. Ascertaining the minimum lethal dose for each animal he experimented on frogs, cats, rabbits, guinea pigs, and other animals, and beginning with one-tenth, one-fifth, or one-half of that dose, and gradually increasing it, he found it possible to administer four or five times, and in the case of rabbits up to even fifty times the lethal dose. From the immunised animal a serum was prepared which was antidotal in very minute quantities if mixed with the venom, but if administered separately by hypodermic injection, though at the same moment with the venom, some twelve and a half times as much was found to be necessary, and it was estimated for a normal bite of an average man no less than 11½ ounces would have to be administered hypodermically soon after the bite to prevent probably a fatal result. The most interesting observation was that the poison taken into the stomach was almost innocuous, and yet exercised a protective effect. In many of the narratives given by travellers describing the feats of the snake charmers it has been related that they will squeeze the venom from the serpent’s mouth and swallow it. This would evidently be one of their methods of rendering themselves proof against the poison when injected by a bite. Professor Fraser’s paper is published in full in “Nature” April 16 and 23, 1896. The author gives his reasons for believing that the action of the antidote is chemical.
Modern Toxicology.
Systematic and scientific investigation of alleged poisoning was scarcely known before the end of the eighteenth or the beginning of the nineteenth centuries. The advance of chemical and physiological knowledge, however, was soon applied to the more certain detection of the criminal use of toxic agents. Orfila’s “Traité de Toxicologie,” published in 1814, the result of a multitude of experiments, was the work which led the way in the establishment of exact tests. Dr. Swaine Taylor in England, Sir Robert Christison in Scotland, Casper in Germany, and a host of other medical chemists pursued the subject, and gradually toxicology reached an assured position. How slow was this attainment may be gathered from the testimony of an expert in a French murder trial in 1823 that globules of fatty mutton had been mistaken for white arsenic.
To Marsh’s arsenic test, made known in 1836, may be traced the practical fall of the poison which for so many centuries had reigned supreme among the deadly agents employed by the most cowardly but most dreaded of the tribe of assassins. The power of proving the presence of the metal which was afforded by the method then set forth brought out the chemical expert, and led to angry controversies. The skilled experimenter was apt to be very confident of his results, and naturally others who claimed to be as skilful as himself disputed his conclusions. Theories of the almost universal diffusion of arsenic were vigorously maintained, and on one occasion in France, in 1839, when Orfila had demonstrated the presence of arsenic extracted from the organs of the person supposed to have been poisoned, Raspail undertook to extract as much from the judge’s armchair.
Meantime the resources of the poisoners had been vastly extended by the discovery of the alkaloids. Many of these substances possessed extreme toxic power, and the invention of the means of detecting them was necessarily a gradual process. It was attained, though; and it may be asserted that at present either by chemical or physiological tests the recognition of the administration of any of the dangerous alkaloids is as certain as is that of the metallic poisons.
About the year 1870 a new complication occurred when an Italian chemist named Dr. Selmi proved that putrefactive animal matter and certain bacteria yielded alkaloidal products, often poisonous, to which the name of ptomaines was given. Selmi was engaged as an expert in the investigation of a case in which it was suspected that an individual had been poisoned. A product was obtained, apparently an alkaloid, but which Selmi could not identify with any known vegetable substance. He came to the conclusion that it was of animal origin, and after a long series of experiments he proved his theory. Several eminent toxicologists at first asserted that ptomaines could be distinguished from vegetable alkaloids by the property of yielding Prussian blue with ferric salts. This test, however, proved fallacious as several series of vegetable alkaloids, notably the pyridic and the allylic, gave the same reaction. The distinction between animal and vegetable alkaloids is a delicate one, and has to be established by an accumulation of chemical evidence.
Leucomaines, which are also alkaloidal products, are distinguished from ptomaines by being formed in the body from living tissues, as a result of their activity. These were first separated by Armand Gautier in 1886. Their constitution is more complex than is that of the ptomaines, but they are not generally of a poisonous character.