FOODS 



119 



constituents and their amounts determined. The absorption apparatus is 

 again weighed. The increase in weight represents the amounts of water 

 and carbon dioxid eliminated and absorbed. The animal is again weighed 

 and the loss in weight noted. 



If at the same time it is desired to collect the heat dissipated .from the 

 body it is necessary to surround the animal chamber with a water jacket, the 

 rise in temperature of which, expressed in calories, indicates the amount of 

 heat dissipated and collected. Since an apparatus of this character de- 

 termines the extent of the respiratory exchange as well as the amount of 

 heat dissipated, it is termed a Respiration Calorimeter. 



For long-continued experiments on animals of large size and on man, 

 one of the larger and more accurately constructed forms of apparatus, such 

 as Benedict's (see Chapter on Animal Heat) must be employed. 



In an experiment to determine the extent of the metabolism in a man 

 during a fasting period there was collected on the first and second days 

 12.17 and 12.84 grams of nitrogen and 188.5 an d *79-4 grams of carbon 

 respectively. From these amounts it was calculated that 76.1 and 80.3 

 grams of protein and 206.1 and 191.6 grams of fat respectively were 

 metabolized. 1 From these figures it is evident that at least equal amounts 

 of protein and fat must be consumed. As a matter of fact, however, these 

 amounts would be insufficient to maintain the energy equilibrium of the 

 body. It has been estimated that at least from 10 to 14 per cent, more 

 food must be added. 



In an experiment made by Vierordt on the customary diet the following 

 results, somewhat rearranged were obtained. On the right, under the term 

 outcome, are arranged the amounts of the substances eliminated; on the left, 

 under the term income, the amounts of the food and tissue principles which 

 were calculated to have been metabolized. If the body is to retain its usual 

 weight it is evident that equivalent amounts of these food principles must be 

 introduced into the body. 



COMPARISON OF THE INCOME AND OUTCOME 



In the foregoing experiment the total nitrogen contained in the urine 

 which was 15.8 grams' is expressed in the table in terms of urea. The chemic 

 composition of urea, COH 4 N 2 taken in connection with the amount stated, 

 indicates that it is the chief end-product of protein metabolism; and as i 

 gram of nitrogen corresponds to 2.14 grams of urea and either to 6.25 grams 

 of protein it is apparent that the urinary nitrogen corresponds to 98.80 grams 

 of protein metabolized. The feces, however, contained 3.3 grams of nitrogen 



1 The amount of the carbon derived from the metabolism of the protein, which in these 

 instances amounted to 40 and 42 grams respectively were first deducted. For each gram of 

 nitrogen present in muscle protein there are 3.28 grams carbon. 



