602 METABOLISM, NUTRITION AND DIETETICS 



In the fat there is, roughly speaking, 12 per cent, of hydrogen, in 

 proteins only 7 per cent. ; so that from three to four times as much 

 hydrogen is contained in the fat of the body as in its proteins. 



Oxygen forms about 12 per cent, of fat, and 20 to 24 per cent, of 

 proteins; the protein constituents of the body, therefore, contain about 

 as much of its oxygen as the fat. 



Of the inorganic salts, calcium phosphate, Ca 3 (PO 4 )2, is much the 

 most abundant, owing to the large amount of it in bone, in the ash of 

 which it is found to the extent of 83 per cent., along with 13 per cent, 

 of calcium carbonate. 



INCOME AND EXPENDITURE OF NITROGEN THE NITROGEN 

 BALANCE-SHEET. 



Nitrogenous Equilibrium. It is a matter of common experi- 

 ence that the weight of the body of an adult may remain approxi- 

 mately constant for many months or years, even when the diet varies 

 greatly in nature and amount. And not only may the weight remain 

 constant, but the relative proportions of the various tissues of the 

 body, so far as can be judged, may remain constant too. Here it 

 is evident that the expenditure of the body must precisely balance 

 its income: it must lose as much nitrogen as it takes in, otherwise 

 it would put on flesh; it must lose as much carbon as it takes in, 

 otherwise it would put on fat. Or, again, the body may be losing 

 or gaining fat, giving off more or less carbon than it receives, while 

 its ' flesh ' (its protein constituents) remains constant in amount, 

 the expenditure of nitrogen being exactly equal to the income.* 

 In both cases we say that the body is in nitrogenous equilibrium. 



A starving animal or a fever patient, on the other hand, is living 

 upon capital, the former entirely, the latter in part ; the expenditure 

 of nitrogen is greater than the income. A growing child is living 

 below its income, is increasing its capital of flesh. In neither case 

 is nitrogenous equilibrium present. 



The starving animal, as long as life lasts, excretes urea, kreatinin, 

 and other nitrogenous substances, and gives off carbon dioxide; 

 but its expenditure, and especially its expenditure of nitrogen, is 

 pitched upon the lowest scale. It lives penuriously, it spins out 

 its resources; its glycogen goes, its fat goes, a certain part of its 

 protein goes, and when its weight has fallen from 25 to 50 per cent, 

 it dies. At death the heart and central nervous system are found 

 to have scarcely lost in weight ; the other organs have been sacrificed 

 to feed them. Fig. 199 shows the percentage loss of weight and 

 the proportion of the total loss which falls upon each of the organs 

 of a cat in starvation (Voit). 



* For long experiments extending over many days the nitrogen balance 

 may be considered as practically the same as the protein balance, but this 

 is not necessarily true of short periods of time, since the stock of nitrogen 

 present in the body in other forms than proteins, although relatively small, 

 is subject to variations. 



