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.