A. Antipyretics, or Drugs which decrease the Bodily Temperature. - There are few if any drugs which can lower the temperature in health. Some, it is true, will cause the temperature to fall below normal, if given to a healthy man in large enough doses to induce severe collapse. The word antipyretic is limited to those drugs which bring down the temperature when it is raised owing to disease. We know that the greatest amount of heat is produced in the muscles, and that there is a special part of the corpus striatum presiding over this production; that heat is lost mostly by radiation from the vessels of the skin and by the evaporation of sweat, and that these vessels and the sudoriparous glands are under the control of the central nervous system. Heat is also lost through the lungs. As the production and loss are in health so accurately adjusted, many observers believe that there is a part of the cerebrum whose function is to maintain the balance between the production and the loss. Also, all parts of this complex mechanism are supplied with bloodvessels, alterations in the calibre of which must affect the activity of the parts they supply.

There is every reason for believing that the part of the central nervous system which presides over the loss of heat (thermolysis), that which presides over the production of heat (ther-mogenesis), and that which possibly presides over the balance between the production and the loss (thermotaxis), can, each of them be influenced by afferent impulses reaching them from various parts of the body, and thus we see each of these three functions can probably be reflexly affected (see diagram on next page).

Antipyretics Which Increase The Loss Of Heat

All sudorifics and all dilators of the cutaneous vessels act as antipyretics. Cold, such as a cold bath, increases the loss of heat by direct abstraction.

Antipyretics Which Increase The Loss Of Heat 155

Drugs Which Probably Diminish The Production Of Heat

Our knowledge about these is at present uncertain, but it is very probable that phenacetin, antipyrin, and acetanilid diminish the production by their action on the corpus striatum; and that quinine, salicylic acid, and salicin, also diminish the production; but we do not know upon what part of the thermo-genetic apparatus they act. A cold bath not only abstracts heat, but, after it has been in operation some little time, diminishes the production.

Antimony, aconite, and digitalis are probably antipyretic through their effect on the circulation, but precisely how they act is not known. Sometimes the removal of some irritation which is acting reflexly may lower the temperature. In this way purgatives are occasionally antipyretics.

Therapeutics

The sole use of antipyretics is to lower the temperature in fever.

Drugs which increase the loss of heat were formerly popular as antipyretics, especially alcohol, spirit of nitrous ether, antimony, ipecacuanha, and opium, but now they are not much used. Cold is more often employed, either by cold sponging, ice, or a cold bath. Sponging with hot water will, by the vascular dilatation and subsequent sweating it induces, reduce a febrile temperature.

Of the drugs which probably alter the production, acetanilid and antipyrin are dangerous because of the collapse they may produce; quinine and salicylic acid are rather uncertain, except in ague and rheumatic fever respectively. Antipyrin and phenacetin are most in demand; they are certain antipyretics. Phenacetin is very safe, but is less powerful. They are quickly absorbed, and so act promptly; they are far more powerful antipyretics than any drugs which act by increasing the loss of heat, and these are very uncertain in their action, often not lowering the temperature at all. Another reason for preferring drugs which diminish thermogenesis is that it is much more rational to lower the temperature by decreasing the production of heat than by increasing the loss, for then the production will, if anything, go on faster than before, in consequence of the attempt to compensate for the increased loss. Antipyretics should be rarely given, for probably fever is often beneficial.

B. Drugs which cause a rise of Temperature. - Belladonna, picrotoxin, and cocaine in poisonous doses may do this. How they act is not known.

Tuberculin, various albumoses and certain animal poisons, such as that of shell-fish, will cause a rise of temperature. Their mode of action is unknown.

We know of no drugs acting on thermotaxis.