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ELEMENTS OF MATERIA MEDICA.

11. Physiological Classes of Medicines.

In order to prevent repetition in the subsequent parts of this work, Ihave thought it necessary to make a few general observations on some ofthe more important and generally admitted physiological classes ofmedicines.

Class 1. Cerebro-Spinants. —I have considered it best to include inone class all those agents whose primary and specific effect is a disorderof one or more of the functions of the cerebro-spinal system (the cere-bral and true spinal systems of Dr. M. Hall). To this class, therefore,are referred all those substances which occasion sleep, insensibility,erroneous perceptions, judgments, and volitions, or delirium, sopor orcoma, paralysis, convulsion, &c.

Some of them produce very slight local effects, as opium ; others occa-sion numbness and tingling, as aconite ; conia causes local paralysis,the substances termed by toxicologists acro-narcotics or narcotico-acrids(as squills, tobacco, foxglove, &c.) when swallowed, occasion inflamma-tion of the gastro-intestinal tube; alcohol, the preparations of arsenic,of copper, of zinc, of bismuth, and of silver, act as powerful localirritants or caustics.

The cerebro-spinants may be thrown into groups or orders founded ontheir effects:—

a. The first group includes those cerebro-spinants which occasiontetanic convulsions, and which have, in consequence, been termed tetanies.Here belong strychnia and brucia, and all substances containing one orboth of these alkaloids, as the seeds of Strychnos Nux vomica ; the barkof this plant (commonly termed false Angustura bark) ; St. Ignatius’sbean ; snake-wood ( lignum colubrinum) ; and the Upas Tieute poison; towhich probably ought to be added the celebrated Tanghin poison. Thesubstances of this order are principally employed in certain torpid orparalytic conditions of the muscular system, under regulations whichwill hereafter be pointed out.

b. The second group is made up of those cerebro-spinants which pro-duce paralysis of the muscles, and is principally composed of conia, analkaloid obtained from hemlock, whose physiological effects would pointit out as the remedy for tetanus, and as the counter-poison for strychniaand brucia, and for the substances containing these alkaloids.

c. The third group includes those agents which occasion paralysis ofthe sentient nerves. Aconite or monkshood belongs to this group. It isthe remedy, therefore, for neuralgia.

d. Tli e fourth group is made up of those agents which, in large doses,occasion sudden loss of sensation and consciousness, with violent con-vulsions; in other words, an epileptic paroxysm. It includes hydrocyanicacid, the cyanurets of zinc and potassium, the bitter almond and its vola-tile oil, and the cherry-laurel and its distilled water. In a concentratedform, and in large doses, hydrocyanic acid sometimes occasions deathwithout convulsions. This order contains the poisons which are themost rapidly fatal of any known. The similarity between the effects oflarge doses of hydrocyanic acid and an epileptic paroxysm are deservingof especial attention : moreover, we ought not to lose sight of the factthat a condition precisely analogous to, if not identical with, this state, isfrequently produced by a large blood-letting. As therapeutic agents, the