PHYSIOLOGICAL CLASSES OF MEDICINES.

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probably be referred to tlie specific effects of these agents on the nervoussystem. And, in the same way, we ought to explain the power of tonicsto increase the tone of the muscular system; for it appears, from Dr.Marshall Hall’s experiments, that one function of the true spinal orexcito-motory system is to give tone to the muscles.

The preparations of arsenic, silver, copper, bismuth, zinc, &c., areusually, but, as I think, most improperly, denominated tonics. They areagents which, in small and repeated doses, as well as in large andpoisonous doses, specifically affect the nervous system, and I havealready noticed them as cerebro-spinants. They have been called tonicsprincipally for the following reason:—cinchona, the most powerful of thevegetable tonics, and in fact the type of the class, has long been celebratedas a curative agent in ague and other periodical diseases; hence it hasbeen assumed that any substances capable of fulfilling the same indica-tion must be possessed of the same properties, and thus arsenic has beencalled a tonic. But the conclusion is erroneous; it is indeed true thatcinchona and arsenic have, in common, the power of curing an ague, butthe same effect is frequently produced by many other very dissimilarsubstances: for example, by bloodletting, by alcohol, and by mentalinfluences. If, therefore, arsenic be a tonic, so also must bloodletting,&c. If we admit this, it follows tonics can no longer be regarded assubstances promoting strength, but merely as agents curing particulardiseases. Before we have any right to associate arsenic among tonics,we must completely alter our definition of these substances, or show thatarsenic improves the appetite and promotes the strength of the body.

Tonics may be arranged in groups, as follow:—

a. The first group includes those vegetable tonics which possessbitterness with little or no astringency; and which have been termed thebitters (amara ), or sometimes the pure or simple bitters {amara pur a seusimplicia). To this group are referred quassia and simaruba, obtainedfrom the order Simarubacece; gentian, American calumba ( Frasera ),chirayita, common centaury, and buckbean, from Gentianaceee; calumbaand Pareira brava from Menispermacettt; and Cetraria Islandica, fromUchenacea. These remedies are employed to promote the appetite andassist digestion in atonic and enfeebled conditions of the stomach ; asgeneral tonics in feebleness and debility of the whole system, and espe-cially of the muscles ; as antipcriodics in intermittent diseases ; and asanthelmintics. Their beneficial operation in expelling intestinal wormshas been referred to their poisonous influence over these parasiticalanimals, but ought perhaps rather to be ascribed to their improvementof the condition of the alimentary canal, and to their removal of thosestates which favour the production of these beings. The power whichbitters possess of retarding the acetous fermentation may, perhaps, con-tribute to their beneficial operation in some dyspeptic cases accompaniedwith acidity and flatulence.

b. The second group comprehends those vegetable tonics whichpossess considerable astringency (from the contained tannic acid) withlittle or no bitterness. These are the pure astringents ( astringentiapura ). In this group are contained oak-bark and nut-galls, fromthe order Cupuliferm; uva ursi, from Ericaceae ; catechu and log-wood, from Leguminosce; rliatany, from Polygalaceee; tormentilla,from Rosacece; the pomegranate-rind, from Myrtacece; bistort, from