638 TEMPERATURE [CH. XLIII. 



his carbon with less than half the heat production of the Esquimaux, 

 who makes blubber his staple article of diet. 



(2) The Seat of Heat Production. So far as our present knowledge 

 goes, the amount of metabolism in the bones, cartilages, and connec- 

 tive tissues is so small as to form but a trifling part of the whole 

 metabolism of the body. The same is probably true of unstriped 

 muscle. Of the coefficient of oxidation (i.e. the amount of oxygen 

 used up per gramme of tissue per minute) of the central nervous 

 system we have no accurate knowledge. Any discussion, therefore, 

 of the principal seats of chemical action in the body resolves itself 

 into a comparison between the glandular and muscular (skeletal) 

 structures. These present a remarkable contrast. The very vascular 

 nature of the secreting glands (the liver is said to contain one-quarter 

 of all the blood in the body), as well as actual measurements of the 

 oxygen used up by many of them, indicate that they are the seat of 

 very active chemical changes, which, relatively to muscle, is maintained 

 with a considerable degree of constancy. The very function which 

 the digestive glands serve implies at least a certain constancy of 

 rhythm. Be the climate what it may, the daily food must be 

 digested. Quite otherwise is it with the muscles. When they are 

 active they are the seat of metabolism as great as that of the glands, but 

 their metabolism is capable of much more complete suspension during 

 rest. When the muscles are inactive the glandular structures, in 

 spite of their smaller bulk, account for a very appreciable quantity 

 of the whole metabolism of the body perhaps as much as half. But 

 when the muscles are exercised to any considerable extent, the con- 

 tribution of the glands becomes an insignificant item in the met- 

 abolism of the body. The muscles, then, by reason of their large 

 mass, and of the great variations of which their metabolism is capable, 

 are essentially the regulators of heat production. 



Apart from active contraction, the muscles differ at different times 

 in tonus. This difference finds its metabolic expression. Zuntz, by 

 cutting the nerves of the already resting leg of a dog, abolished the 

 muscular tonus and greatly lessened the metabolism. Alterations 

 in tonus probably play a very important part in the production of 

 heat. Our muscles are "braced" in cold and "slack" in warm 

 climates. The latter effect is very strikingly shown by the extreme 

 muscular flabbiness which evinces itself in such a climate as that of 

 the Ked Sea. Where the cold is such that increased tonus proves 

 inadequate to meet the demand for heat, a greater degree of muscular 

 activity (shivering) supervenes unless actual exercise is taken. 



Heat Loss. 



The two channels of loss susceptible of any amount of variation 

 are the lungs and the skin. The more air that passes in and out 



