GENERAL METABOLISM 



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half times as much carbon as nitrogen, and hence, when they 

 are broken down, for each grm. of nitrogen excreted, 34 grms. 

 of carbon are given off. 



The carbon is chiefly excreted from the lungs as carbon 

 dioxide, and in this form it may be collected and estimated. 



Any excess of carbon excreted, over the 3'4 times the amount 

 of nitrogen given off, must be derived from the fats of the body 

 or from the fats and carbohydrates taken in the food. Any 

 carbon retained in the body, apart from that in proteins, is 

 stored ultimately as fat. Since carbon constitutes 76'5 per 

 cent, of fats, the amount of fat is calculated by multiplying 

 the carbon by 1*3. 



The following tabular example of an investigation of the 

 metabolism may be given : 



Two grins, of nitrogen are retained as protein ; that is, 2 x 

 6 '25 = 12'5 grms. of protein are being daily laid on. Thirty 

 grms. of carbon are also retained in the body, and of this 3'4 x 

 2 = 6'8 grms. are combined with the nitrogen in the protein. 

 The remainder, 23'2 grms., go to form fats, the amount of which 

 is 23-2 x 1-3 = 3016 grms. of fat. 



2. Metabolism during Fasting 



When the usual supply of energy in the food is cut off, the 

 animal liberates the energy required by oxidising its own stored 

 material and ife tissues. This is shown by the fact that the 

 animal loses weight and goes on excreting carbon dioxide, 

 urea, and the other waste products of the activity of the 

 tissues. 



Several prolonged fasts have been undertaken by men, and, 

 in one or two of these, careful observations have been made by 

 physiologists. It has been found that during the first day or 



