60-i METABOLISM 



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

 available 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 699). The glycogen content of the skeletal muscles becomes 

 reduced but not that of the heart. 



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 only amounts to between 20 

 and 50 per cent at the time of death by starvation, it is unlikely that gen- 

 eral failure can be the 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 

 material for the elaboration of some substance (hormone) necessary for 

 life, or because they 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 the balance sheet of a business concern showing an excess of 

 expenditure over income could be adjusted in this way. But it is a very 

 different matter with the nitroycn balance sheet of the body; for, if we 

 give the starving animal just enough protein but no other foodstuffs to 

 eover the nitrogen loss, we shall cause the excretion to rise to a total 

 which is practically equal to the starvation amount phis all that we have 

 given as food ; and although by daily giving this amount of protein there 

 may be a slight decline in the excretion, it will never become the same as 



