THE HEAT OF THE BODY. 485 



is still undecided. Certain phenomena of disease, however, 

 seem to render their existence probable. If we return for a 

 moment to our former comparison of the working Body to 

 a steam-engine, such nerves might be regarded as agencies 

 increasing its rate of rusting without setting it at work. 

 The oxidation of the iron would develop some heat, but by 

 processes useless to the steam-engine, although such are, in 

 moderation, essential to living cells; the vitality of these, 

 even when they rest, seerns to necessitate a constant, if small, 

 breaking down of their substance. In an amoeboid cell no 

 doubt such processes occur quite independently of the ner- 

 vous system; but in more differentiated tissues they may be 

 controlled by it. Just as a muscle does not normally con- 

 tract unless excited through its nerve, although a white 

 blood-corpuscle does, so may the natural nutritive processes 

 of the muscle-fibre in its resting condition be dependent on 

 the nerves going to it. If these be abnormally excited the 

 muscle will break down its protoplasm faster than it con- 

 structs it, and consequently waste; at the same time the 

 increased chemical degradation of its substance will elevate 

 its temperature. Febrile conditions, in which many tissues 

 waste, without any unusual manifestation of their normal 

 physiological activity, would thus be readily accounted for 

 as due to superexcitation of the thermogenic nerves and 

 nerve-centre. 



The condition of fever or pyrexia, as an abnormally high 

 temperature is named, could conceivably be brought about by 

 increased heat production, decreased heat loss, or both; or 

 by a greater increase of production than of loss. Direct ex- 

 periments on animals prove that there is always increased 

 production of heat, in febrile diseases. This is shown by the 

 fact that the animal uses more oxygen and gives off more 

 carbon dioxide in a given time than when in health. It also 

 usually gives off more heat, but not enough to compensate for 

 the increase of oxidative processes going on in its body, and 

 so its temperature rises. The regulating mechanism which 

 in health keeps heat production and heat dissipation propor- 

 tionate is out of gear. As regards the increased heat formation 

 in pyrexial conditions, there is some reason to believe that it 

 is usually due to excitation by morbid products of thermogenic 

 centres lying in the corpora striata or optic thalami. Prick- 

 ing those regions of the brain of an animal causes greatly in- 





