PHYSIOLOGICAL EFFECTS OF MEDICINES.

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b. Chemical or Ckemico-vilal effects, as those produced by the agentsdenominated caustics. The constituents of the tissues on which thecaustics expend the energy of their affinities are principally water,albumen, fibrin, and gelatine. Water constitutes four-fifths of the weightof the animal tissues and without it, they are wholly insusceptible ofvitality, except in the case of some of the lower animals. — ( Muller'sElem. of Physiol, p. 7.) Hence, therefore, agents like sulphuric acid,which powerfully attract water, act as caustics. Substances which eithercoagulate liquid albumen, as the mineral acids and alcohol, or whichdissolve solid albumen, fibrin, and gelatine, as the alkalis, are alsopowerful caustics. Many salts, as bicliloruret of mercury, sulphate ofcopper, acetate oflead, and chloruret of zinc, form new compounds whenplaced in contact with the organic principles just referred to : they alsoare caustics. As a preliminary to the production of the chemical changeshere mentioned, the caustic must destroy the life of the part. Lastly,around the cauterized parts inflammation is set up.

c. Vital Effects. —The effects placed under this head are those whichare unaccompanied by any obvious mechanical or chemical changes.As examples we may select two kinds—the vascular and nervous.

The vascular effects are those caused by the agents termed irritants oracrids, as cantharides, savine, gamboge, croton oil, &c. They are, pain,heat, redness, and the other phenomena of inflammation.

The nervous effects are numbness, tingling, pricking, and sometimesparalysis, without necessarily any redness or other obvious change in thevascular conditions of the part. When a few drops of the tincture of theroot of aconite are applied to a delicate part of the skin, as the inner sur-face of the lips, numbness and tingling are speedily experienced. Themost powerful effects are produced by the Aconitum ferox, a native ofNepal , and used as a poison under the name of Bish or Bitch. Some yearsago, at the request of Dr. Wallicli, I undertook a series of experimentsto determine its effects, (see his Plantee Asiatics rariores). I foundthat one drop of the alcoholic tincture of the root applied to the tongue,caused, within ten minutes, intense numbness in the tip of that organ,and also in the lips, with a sensation as though the soft palate and uvulawere relaxed and rested on the tongue. The latter symptom continuedfor about 15 minutes only, but the numbness and tingling endured for18 hours.

2. Remote Effects. —These are of two kinds, chemical and vital.

a. Chemical effects. —Vogt ( Pharmakodynamik , bd. i. p. 15) denies thatany remote chemical effects can be produced. But for the reasonsbefore detailed, I regard the alteration in the qualities of the urine, bythe internal use of acids or alkalis, as the effect of chemical influence.Moreover, the deposition of silver under the skin by the exhibition of thenitrate, and the colour communicated to bones by the use of madder,seem to show that even solids may undergo chemical changes by theinternal employment of medicines.

b. Vital effects. —The functions of remote parts are affected by medi-cines, as when narcotics or diuretics are exhibited:—The former act onthe brain, the latter on the kidneys. Inflammation even may be set upin a distant organ,—as of the bladder, by the use of cantharides.