570 METABOLISM 



the presence of an amount of amino nitrogen not much below that of 

 normal animals (viz., 4 mg. per 100 c.c. of blood). Similarly with 

 carbohydrates, early in the condition the blood sugar becomes much 

 lower than normal, but then remains steady. This is significant when 

 we remember that after two or three days of starvation all of the avail- 

 able glycogen has been used up. It indicates that carbohydrate must 

 be essential for life, and that it is produced in starvation from proteins 

 (see page 667). 



Starvation ends in death in an adult man in somewhat over four 

 weeks but much sooner in children, because of their more active metab- 

 olism. At the time of death the body weight may be reduced by 50 per 

 cent. The body temperature does not change until within a few days 

 of death, when it begins to fall, and it is undoubtedly true that if means 

 are taken to prevent cooling of the animal at this stage, life will be 

 prolonged. 



Death from starvation must be due either to a general failure of all 

 the cells or to injury of certain organs that are essential for life. Since 

 the loss of protein from the body as a whole may vary between 20 and 

 50 per cent at the time of death by starvation, it is unlikely that general 

 failure can be its cause. If it were so, death would always occur when 

 some fixed loss of protein had occurred. Certain organs evidently cease 

 to perform their function, either because they are deprived of raw mate- 

 rial for the elaboration of some substance (hormone) necessary for life, 

 or because the organs themselves wear out from want of nourishment. 



NORMAL METABOLISM 



Apart from the practical importance of knowing something about the 

 behavior of an animal during starvation, such knowledge is of great 

 value in furnishing a standard with which to compare the metabolism 

 of animals under normal conditions. Taking again the nitrogen balance 

 as indicating the extent of protein wear and tear in the body, let us 

 consider first of all the conditions under which equilibrium may be re- 

 gained. It would be quite natural to suppose that, if an amount of pro- 

 tein containing the same amount of nitrogen as is excreted during 

 starvation were given to a starving animal, the intake and output of 

 nitrogen would balance. We are led to make this assumption because we 

 know that any business balance sheet showing an excess of expenditure 

 over income could be met by such an adjustment. But it is a very differ- 

 ent matter with the nitrogen balance sheet of the body; for, if we give 

 the starving animal just enough protein to cover the nitrogen loss, we 

 shall cause the excretion to rise to a total which is practically equal to 



