- drophobia it is well shown that the narcotic action of opium is not
produced even by large doses often repeated.—The same state occurs in excessive hemorrhage.
In the operation of this class of modifying agents it is a general law, to which there are probably few exceptions, that they chiefly affect poisons of the organic kingdoms, and the narcotics above all. At least in the instance of most mineral poisons their influence is very inferior. Their operation may be accounted for in various ways. Sometimes, as in dysentery and cholera, the poison is carried with unusual rapidity through the alimentary canal. Sometimes again it remains comparatively inert, because on account of the impaired activity of absorption, it is not taken up with the usual quickness by the absorbent vessels. And sometimes, as in the instance of tetanus, mania, and rabies, the nervous system is in a state of peculiar excitement, by which the customary action of the poison is in a great measure, if not entirely, counteracted.
In a few diseased states of the system there is an increased susceptibility of the action of poisons: and it is important that the medical jurist should attend to this circumstance. When a poison has a tendency to bring on a peculiar pathological state of the system, or of a particular organ, which state is also produced by a disease existing at the time or impending, violent and even fatal consequences may ensue from doses of poisons which in ordinary circumstances are innocuous or beneficial. Thus in persons affected with apoplexy an ordinary dose of opium may accelerate death; and in people even with a mere tendency to apoplexy, if it is strongly marked, or appears from what are called warning symptoms to be on the point of developing itself, a common dose of such narcotics as occasion determination to the brain may excite the apoplectic attack. Thus, too, in cases of inflammatory disorders of the alimentary canal, irritating substances, in doses not otherwise injurious, may produce dangerous impressions on the tender membrane with which they come in contact. But in respect to this last example, it must be remarked, that the improvements or the caprice of medical practice have gone directly in face of the rule, by suggesting that some internal inflammations of the alimentary canal may be successfully treated with irritating remedies.
I might here perhaps have added among the causes which modify the action of poisons, sleep, and the administration of other poisons. The latter subject, however, will be better considered at the end of the Individual Poisons, under the title of Compound Poisoning. The former agent is of doubtful effect. Some observations on its influence will be found in the chapter on the Evidence of General Poisoning, p. 41.
Application of the preceding remarks to the Treatment of Poisoning. As an appendix to what has been said respecting the physiological action of poisons, and the causes by which it is liable to be modified, I shall here state shortly certain applications to the treatment of poisoning.
