176 HUMAN PHYSIOLOGY 



respiratory exchange of gases is considerably decreased. 

 Besides, during sleep the muscular movements, except those 

 of the heart and respiratory muscles, are reduced to a mini- 

 mum, and the muscle tonus also, which maintains the position 

 of the body, is inhibited. The proteid metabolism is not 

 affected by sleep. 



It has not yet been definitely proven that psychical activity 

 has any effect upon metabolism. 



III. Effect of the size of the body, age, and sex upon 

 metabolism. Small persons have a relatively greater meta- 

 bolism than large persons, for, since in them the surface by 

 which heat is lost is larger in proportion to the heat-produc- 

 ing mass than in large individuals, the smaller person must 

 produce relatively more heat in order to keep a constant 

 body temperature than the larger person. Hence the 

 metabolism of a child is relatively greater, although abso- 

 lutely smaller than that of the adult (see page 1 1 8). In old 

 age the metabolism is smaller than in the prime of life. 

 Because of differences in the size of body, the metabolism in 

 a woman is less than in a man, therefore the diet for woman 

 is also less. An adult, resting woman needs 90 g proteids, 

 40 g fat, and 350 g carbohydrate daily. During pregnancy 

 the metabolism is increased. Sex itself has no influence 

 upon metabolism. 



