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ELEMENTS OF MATERIA MEDICA.

eluded those medicinal agents which diminish the temperature of thebody when pretematurally increased. The only agent which in all casesreduces animal heat is cold, used in the form of ice, cold air, cold baths,cold lotions, cold drinks, &c. Its agency is obvious: it abstracts heat,and thereby lowers the intensity of the vital movements, diminishes vas- :cular action, and reduces the calorific functions. But there are certainmedicinal substances which, by continued internal use, allay febrile heat,and usually promote the secretions, though they have no power of dimi-nishing the ordinary or healthy temperature, and to these the term refri-gerant (or temperant) is usually applied. How they act is not com-pletely understood. Dr. Murray thought they furnished oxygen to thesystem, and in that way prevented so large a quantity of it being con-sumed in the process of respiration,—an explanation borne out by theobservations of Mr. Spalding and Dr. Fyfe, that vegetable diet reducesthe consumption of oxygen gas in respiration.

Refrigerants may be arranged in the following groups :—

a. The first group contains the mineral and vegetable (sulphuric, hy-drochloric, acetic, citric, tartaric, &c.) acids, as well as the acid- or super-salts (alum and bitartrate of potash).

b. The second group includes certain neutral salts; namely, the nitrateand chlorate of potash.

c. The third group comprehends certain fruits (as oranges, lemons,mulberries, tamarinds, prunes, fruit of the dog-rose, &c.), and herbs (aswood sorrel, common sorrel, lettuce, &c.)

d. The fourth group comprises the animal refrigerants ; as hutter-milk{lac ebutyratum ), and acid whey ( serum lactifs acidum).

Class 6, Evacuants. —These are medicinal agents which provoke adischarge by some emunctory. They are tenned vito-secerning agentsby the late Dr. Nuttall ( Lancet , vol. ix. for 1825-26, p. 578); and vitalagents which operate on the secerning system, by Dr. A. T. Thomson{Elements of Materia Medica and Therapeutics)

Evacuants act by the skin (diaphoretics or sudorifics); by the mucousmembranes (errliines, expectorants, emetics, cathartics, emmenagogues);by the glands (diuretics, sialogogues).

1. Diaphoretics or Sudorifics. —Therapeutic agents, which promotethe cutaneous transpiration, are called either diaphoretics or sudorifics.When the insensible perspiration is increased, they are tenned diapho-retics {diaphoretica, from luttpoplu, to transpire) : when sensible perspira-tion or sweat is augmented, they are called sudorifics {sudorifica, from ;sudor, sweat, and facio, I make.) But most modem physiologists regardthe insensible perspiration and the sweat as productions of the same set (of vessels, and as differing only in their physical form: the one existingas a vapour, the other as a liquid. In fact it is supposed that if thecutaneous transpiration be moderate, it is converted into vapour as fastas it is fonned, and hence is termed the insensible perspiration. If,however, it be exhaled more quickly than the atmosphere can take it up,an accumulation is the result, and it appears on the skin in the form ofdrops, called sweat. Adelon {Physiologie, tom . iii. p. 517, ed. 2nde),however, states that sweat contains less carbonic acid, and more salts,than the insensible perspiration; but the correctness of this assertion isvery questionable, on account of the difficulty of obtaining the insensibleperspiration for comparison, and, perhaps, from its properties varying at i