202 ELEMENTARY PHYSIOLOGY less. 



cold than its interior. Nevertheless, the temperature 

 of the body is in health maintained very evenly, at 

 all times and in all parts, within the range of two 

 degrees or even less on either side of 37^ C (98*6° 

 Fahrenheit). 



This is the result of three conditions : — the first, that 

 heat is constantly being generated in the body ; the 

 -second, that it is as constantly being distributed through 

 the body ; the third, that it is subject to incessant 

 regulation as regards both loss and production. 



Heat is generated vvlienever oxidation takes place. As 

 we have seen, the tissues all over the body, muscle, brain- 

 substance, gland-cells and the like, are continually under- 

 going oxidation. The living substance of the tissue, built 

 up out of the complex proteins, fats, and carbohydrates, 

 and thus even still mure complex than these, is, by means 

 of the oxygen brought by the arterial blood, oxidised, and 

 broken down into simpler more oxidised bodies, which 

 are eventually reduced to urea, carbimic acid, and water. 

 Wiierever life is being manifested these oxidative changes 

 are going on, more energetically in some places, in some 

 tissues' and in some organs, than in others. Hence every 

 capillary vessel and every extra-vascular islet of tissue is 

 really a small fireplace in wliich heat is being evolved, in 

 proportion to the activity of the chemical changes which 

 are going on . 



The chief seat of this heat production is undoubtedly in 

 the muscles ; for, as already pointed out, they make up 

 about half the body-weiglit, and are carrying on an active 

 oxidation even while at rest. This gives rise to heat, and 

 wlicn a muscle enters into a state of contracting activity, 

 the heat production becomes so rapid as to produce an 

 actual measurable rise »of its temperature. After the 

 muscles we may regard the liver and the other secreting 

 glands as the next great heat-producing organs of the 

 body. 



But as the vital activities of different parts of the 



