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 excessive exhaustion and insensibility. A similar inquiry was instituted about the same time by M. Devergie, who seems, however, to have remarked more activity in alum than is indicated by Orfila's experiments. He infers that two ounces may sometimes kill dogs, even though they vomit freely; that half that quantity is fatal if the gullet be tied; that calcined alum is more active than a solution of the salt; that it is a corrosive or irritant; and that probably man is more sensible to its operation than the lower animals. Whatever may be thought of the effects of alum on the animal body when administered in large doses, it is plain from its frequent medicinal use as an internal astringent that it is not poisonous when given in small doses, like that taken by the patient in the trial alluded to. I may add that it appears very doubtful whether any injury accrues from the long-continued use of very small doses. Bakers, it is well known, are in the practice of using it in minute proportion for improving the whiteness of bread; and it has been imagined that chronic disorders of the stomach and bowels may consequently originate, by reason of its constipating tendency. These fears, however, are not borne out by facts. Either the quantity is insufficient to do harm in the way supposed; or the constitution becomes accustomed to the continual operation of the salt, and does not suffer.

CHAPTER XXIV.

CLASS SECOND.

OF NARCOTIC POISONS GENERALLY.

The term narcotism has been used by different writers with different significations, but is now generally understood to denote the effects of such poisons as bring on a state of the system like that caused by apoplexy, epilepsy, tetanus, and other disorders commonly called nervous. Narcotic poisons, therefore, are such as produce chiefly or solely symptoms of a disorder of the nervous system.

The mode in which most narcotic poisons act has been well ascertained: they act on the brain or spine or both by entering the blood-vessels. Hence they are most active when most directly introduced into the blood, that is, when injected into the veins; and when they are applied to an entire membranous surface, their energy is in the ratio of its absorbing power. Thus, when injected into the chest, they act more rapidly than when swallowed. According to the generally received opinion, they are conveyed with the blood to the brain and spine on which they act. But, according to the views of Messrs. Morgan and Addison, they produce on the inner coats of the blood-vessels a peculiar impression, which is conveyed to the centre of the nervous system along the nerves.