158 HUMAN PHYSIOLOGY 



The salts of the income and outgo are determined in the 

 ash. 



The water is generally accounted for as such in the 

 balance of nutrition. 



To be of any value in judging the metabolism of the body, 

 the experiments on metabolism must be carried on for an 

 extended period. Unless otherwise indicated, the results of 

 such experiments are calculated upon a basis of twenty-four 

 hours. 



2. THE VALUE OF THE RESULTS OF EXPERIMENTS 

 IN METABOLISM 



Determination of the carbon furnishes the basis for study- 

 ing the history of all the organic foodstuffs in the body. If 

 carbon equilibrium is obtained, i.e. if as much carbon is 

 taken up as is given off, as great a quantity of organic sub- 

 stances is consumed in the body as is taken up. If more 

 carbon is taken up than is given off, the body stores up 

 organic substances ; but if more is given off than is taken up, 

 the body loses some of its organic constituents. 



Determination of the nitrogen affords us information as to 

 the proteids in the body, for all the nitrogen of the income 

 is contained in the proteid. As the proteids contain on the 

 average \6% nitrogen, the amount of nitrogen found, multi- 

 plied by 6.25, gives the corresponding amount of proteid. 

 If the amount of proteid decomposed in the body is equiva- 

 lent to that taken up, the body is in nitrogenous equilib- 

 rium. If more nitrogen is taken up than is given off, flesh 

 is formed. But if the body gives off more nitrogen than it 

 takes up, it loses some of its proteids. 



The proportion of the nitrogen to the carbon in the pro- 

 teids is as I : 3.3. From the estimated nitrogen of the in- 

 come and outgo, it can be calculated, by means of these 

 figures, how much of the carbon of the income and outgo 

 is derived from proteids. If the amount of carbon derived 

 from the proteid is subtracted from the whole quantity of 



