- sidering the crude methods of analysis formerly trusted to, and the
obstacles opposed to the successful application of them by the presence of organic matter, there can be no wonder that chemists, even but a few years ago, could not satisfy themselves whether the objects they were in search of had been detected or not. Then, it was partly known before, and is now fully established, that various poisons are removed beyond the reach of analysis before death, in consequence of passing off with the secretions, particularly the urine. Farther, it seems probable that, of the poisons which act through absorption, several do not remain or at least do not accumulate, in the blood; and that they are not distributed with it throughout the textures indifferently, but are deposited, as absorption goes on, in particular organs, such as the liver,—which it was not much the practice to examine in former investigations. And lastly, some poisons are speedily decomposed on entering the blood: They either cause obvious changes in the constitution of the blood, and themselves undergo alteration likewise; or without the blood becoming appreciably different in its properties from the healthy state, the poison undergoes a rapid change in the molecular affinities of its elements, and so disappears. Of the former course of things distinct illustrations are furnished by nitric oxide gas and sulphuretted-hydrogen gas when injected into a vein in a living animal: of the latter an equally unequivocal example occurs in oxalic acid, which Dr. Coindet and I found to be undiscoverable in the blood of the vena cava of a dog killed in thirty seconds by the injection of eight grains and a half of it into the femoral vein.
But the improvements that have been lately made in the methods of analysis for the detection of poisons in a state of complex mixture with organic substances have done away with a great part of the obstacles which prevented a thorough inquiry as to the existence of poisons in the blood and textures of the body. Some important researches of this kind were referred to in the last edition of the present work; and since then many additional facts, of equal variety and precision, have been communicated by different observers, but especially by Professor Orfila. Under the head of each poison an account will be given hereafter of the evidence in support of the discovery of it by chemical analysis in the blood, textures, and excretions. In the present place it is sufficient to state in general terms that the evidence is quite satisfactory in the instances of iodine, sal-ammoniac, oxalic acid, nitre, sulphuret of potassium, arsenic, mercury, copper, antimony, tin, silver, zinc, bismuth, lead, hydrocyanic acid, cyanide of potassium, carbazotic acid, sulphuretted-hydrogen, camphor, and alcohol.
Of the Organs affected by the remote action of Poisons.—Having now taken a general view of the mode in which poisons act on distant parts, I shall next consider what organs are thus brought under their operation. Poisons have been often, but erroneously, said to affect remotely the general system. A few of them, such as arsenic and mercury, do indeed appear to affect very many organs of the
