Page:Treatise on poisons in relation to medical jurisprudence, physiology, and the practice of physic (IA treatiseonpoison00chriuoft).pdf/545

 red colour struck by perchloride of iron with the meconic acid. Now, will this alone constitute sufficient proof of the presence of opium? On the whole, I am inclined to reply in the affirmative. Sulphocyanic acid, it is true, has the same effect, and this acid has been proved by Professors Gmelin and Tiedemann to exist in the human saliva, —a fact which was called in question by Dr. Ure in his evidence on the trial of the Stuarts, but which at the time I had verified, and which Dr. Ure has since been compelled by experiments of his own to admit. But it must be very seldom possible to procure a distinct blood-red coloration from the saliva, after it has been mixed with the complex contents of the stomach, and subjected to the process of analysis detailed above; and the check proposed by Dr. Percy (p. 532) will distinguish it.

II.—Of the Action of Opium, and the Symptoms it excites in Man.

The symptoms and mode of action of opium have been long made the subject of dispute, both among physicians and toxicologists; and in some particulars our knowledge is still vague and insufficient.

Under the head of general poisoning, some experiments were related, from which it might be inferred that opium has the power of stupefying or suspending the irritability of the parts to which it is immediately applied. The most unequivocal of these facts, which occurred to Dr. Wilson Philip, was instant paralysis of the intestines of a dog, when an infusion of opium was applied to their mucous coat; another hardly less decisive was palsy of the hind-legs of a frog, observed by Dr. Monro Secundus, when opium was injected between the skin and the muscles; and a third, which has been remarked by several experimentalists, is immediate cessation of the contractions of the frog's heart when opium is applied to its inner surface.

The poison has also powerful constitutional or remote effects, which are chiefly produced on the brain. Much discussion has arisen on the question, whether these constitutional effects are owing to the conveyance of the local torpor along the nerves to the brain, or to the poison being absorbed, and so acting on the brain through the blood. The question is not yet settled. It appears pretty certain, however, that the poison cannot act constitutionally without entering