Page:Treatise on poisons in relation to medical jurisprudence, physiology, and the practice of physic (IA treatiseonpoison00chriuoft).pdf/20

 clear, however, that nervous transmission is in such circumstances the only possible medium of action; and that the phenomena may not as well be owing to the agent being conveyed in substance, by imbibition or absorption, to the parts ultimately acted on. It is not unworthy of remark too, that in the case of hydrocyanic acid,—a poison, which, more perhaps than any other, has been held to act by sympathy, and which produces on the integuments a direct local impression of a peculiar and unequivocal kind,—there is positive evidence of the direct impression not being conveyed along the nerves, even to the most limited distance; for I have not been able to observe the slightest effect beyond the abrupt line on the skin which defines the spot with which the acid had been in contact.

Secondly, it is thought that certain poisons, such as hydrocyanic acid, strychnia, alcohol, conia, and some others, produce their remote effects with a velocity, which is incompatible with any conceivable mode of action except the transmission of a primary local impulse along the nerves, and more especially incompatible with the poison having followed the circuitous route of the circulation to the organs which are affected by it remotely. Thus in regard to the hydrocyanic acid, Sir B. Brodie has stated, that a drop of the essential oil of bitter almonds, which owes its power to this acid, caused convulsions instantly when applied to the tongue of a cat; and that happening once to taste it himself, he had scarcely applied it to his tongue, when he felt a sudden momentary feebleness of his limbs, so that he could scarcely stand. Magendie, speaking of the pure hydrocyanic acid, compares it in point of swiftness of action to the cannon ball or thunderbolt. In the course of certain experiments made not long ago with the diluted acid by Dr. Freer, Mr. Macaulay and others, to decide the true rapidity of this poison, several dogs were brought under its influence in ten, eight, five, and even three seconds; during an experimental inquiry I afterwards undertook for the same purpose, I remarked on one occasion that a rabbit was killed outright in four seconds; and Mr. Taylor has more recently stated, that he has seen the effects induced so quickly in cats, that there was no sensible interval of time between the application of the poison to the tongue and the first signs of poisoning. Strychnia, the active principle of nux-vomica, acts sometimes with a speed little inferior to that of hydrocyanic acid; for Pelletier and Caventou have seen its effects begin in fifteen seconds. Alcohol, according to Sir B. Brodie, also acts on animals with equal celerity; for when he introduced it into the stomach of a rabbit, its effects began when the injection was hardly completed. Conia, the active principle of hem-*