l8o NUTRITION, DIETETICS AND ANIMAL HEAT 



During sleep the nitrogenous output is not materially dimin- 

 ished, while that of CO 2 is markedly less. This is explained by 

 the fact that there is less energy needed and correspondingly 

 less oxidation of the energy-producing materials. Proteid 

 metabolism is undisturbed. 



A low external temperature does not increase the output of 

 urea; it increases the output of CO 2 . These two facts together 

 mean again that only the carbohydrates and fats are being oxi- 

 dized in increased amount. This increased oxidation, the effect 

 of which is to maintain the normal body temperature is usually 

 dismissed with the statement that it is a reflex nervous act. It is 

 claimed by Johannson that the CO 2 output is not increased until 

 shivering occurs (Reichert). That being the case, the increase is 

 explained on the ground of increased energy and heat production 

 incident to muscular exercise, and shivering assumes the dignity 

 of a physiological factor in keeping up the temperature of the 

 body. This is perfectly reasonable when it is remembered how 

 effective active muscular exercise is in keeping the body warm. 

 But the fact that a person when cold shivers and is restless invol- 

 untarily does not allow us to escape the unsatisfactory "reflex 

 action" explanation of the phenomenon in question. Within 

 ordinary and reasonable limits proteid metabolism is undis- 

 turbed; it is still being protected by the fats and carbohydrates. 



During starvation nothing is supplied from the outside world 

 except oxygen, and the animal must live on the materials al- 

 ready in his body. The glycogen is first consumed; it is the 

 surplus on hand; but at best it is all gone in a very few days. 

 Then the fat stored up as adipose tissue is drawn upon; it is the 

 reserve fund; but it is likewise soon consumed; the animal be- 

 comes progressively emaciated. When this is exhausted the 

 tissue proteid is attacked; this is the capital and is the last to be 

 touched; but there must be heat and at least some energy, and 

 there is no other source. When the proteid capital has at last 

 been so impaired that it can no longer furnish heat to maintain 



