148 METABOLISM 



and amount. It is inferred, and correctly, that the relative 

 proportions of the different tissues of the body remain constant 

 too. Under such conditions the expenditure of the body must 

 exactly equal its income; otherwise, the balance would not 

 be maintained. If the body retains more nitrogen than it 

 gives off, it must be accumulating protein; if it retains more 

 carbon than is given off, it must be storing glycogen or fat, 

 and in either case the body must increase in weight. But 

 whether or not the body may be losing or gaining fat, giving 

 off more or less carbon than it receives, as long as the expendi- 

 ture of the nitrogen is exactly equal to the income, then the 

 body is said to be in nitrogenous equilibrium. 



A starving animal or a fever patient, entirely or in part, 

 live upon their own body tissues and are losing nitrogen. A 

 growing child increases its store of nitrogen. In neither case 

 is there nitrogen equilibrium. An animal in starvation excretes 

 kreatinin, urea, and other nitrogenous substances and gives 

 off carbon dioxide, but all expenditures are reduced to a mini- 

 mum. When its weight has fallen from 25 to 50 per cent., 

 it dies. Muscles suffer most absolutely, and fats most relatively 

 while organs in continuous activity, like the heart and central 

 nervous system, lose practically nothing. During the first 

 day of starvation the excretion of urea is not altered, since it 

 requires about twenty-four hours for the elimination of the 

 protein of the last meal. The excretion of urea then rapidly 

 sinks to a low, constant amount, which is maintained until 

 a short time before death, when there may be either a rapid 

 decline or a brief premortal increase. The duration of starva- 

 tion depends upon the reserve store of material which the 

 animal possessed. Fats, for instance, economize the proteins 

 of a starving animal, but however much fat there may be, 

 the steady loss of tissue protein goes on. If sugar or sugar 

 and fat are given, the premortal rise in urea excretion does 

 not take place, and the excretion of nitrogen may be reduced 

 to one-third of the amount when no food at all is given. In 

 this way the daily excretion of nitrogen in man has been reduced 

 to four grams. Fat and carbohydrate are much more effective 

 in sparing f protein than is fat alone. This is because living 

 matter 'needs sugar, and when not supplied protein is destroyed 

 to furnish it. 



