296 Influence of Inanition on Metabolism. 



<!i.-tributed among the different days in proportion to the nitrogen ingested. 

 These apportionments are given in the second column of the table. The 

 average fecal excretion of nitrogen per day for each week is also recorded. 



Heat of combustion of food, feces, and urine. The larger portion of the 

 potential energy of the food ingested is either liberated in the form of heat 

 as a result of oxidation in the body or stored as potential energy of body 

 material, but a small portion of the potential energy of food leaves the body 

 unoxidized in the organic matter of feces and urine. The proportion of the 

 total energy unavailable for use by the body can be found by determining the 

 heat of combustion of the organic matter of feces and urine. The determi- 

 nation of the heat of combustion of food or indeed of feces presents little 

 difficulty, and as has been stated before the heat of combustion of the dry 

 matter of food for each day and the feces for each week was determined on 

 all the samples in these experiments. On the other hand, considerable difficulty 

 is experienced in obtaining accurate results for the heat of combustion of urine 

 and the process is much longer since the urine must be dried, preferably in a 

 vacuum at room temperature. Many experiments made in this laboratory and 

 indeed some experiments with this same subject S. A. B., have shown that 

 the energy of the urine can be approximately computed by allowing 9 calories 

 for every gram of urinary nitrogen. Hence in the experiments under dis- 

 cussion the energy of the urine was calculated by the use of this factor and 

 the total nitrogen of the urine. Direct determinations of the heat of com- 

 bustion of urine were made on a few samples. 



Table 182 shows the determined heats of combustion of the food and feces, 

 and the calculated heats of combustion of the urine, from which data the 

 available energy (given in column d) for each day of the experiments is 

 derived. As stated above the energy of the urine is calculated, and owing to 

 the impracticability of making determinations on daily samples of feces 

 the heat of combustion of the feces for each day has been obtained by means of 

 the weight of partially dried material (table 179), and the heat of combustion 

 per gram of the total for the week. Appended to the table are notes showing 

 the few actual determinations of the heat of combustion of urine. 



A comparison of the calculated amounts of energy in the urine with corre- 

 sponding amounts actually determined shows not inconsiderable variations. 

 For the purpose for which the energy of the urine is obtained, however, the 

 errors involved make no material difference in the results. The largest error, 

 19 calories on March 18-19, constitutes only about 0.3 per cent of the total 

 energy of food. 



Analysis of urine. The determinations in the urine that are of especial 

 value in an experiment of this nature were made and the results are recorded 

 in table 183. The weight, specific gravity, and volume are of interest for 



