9 



slum bicbromate, 25 cubic centimeters of the milk used at each meal. 

 In the experiments of 19(»l-3 the amount of milk reserved at each 

 meal was 60 cubic centimeters. The temperature of the drying oven 

 was kept at about 6(P C. in all cases of the determination of moisture 

 in the feces. The bread was also dried at this temperature. Nitrogen 

 was determined by the ordinary Kjeldahl process. In the case of 

 wheat and its milling products and bread, protein was obtained by 

 multiplying nitrogen by the factor 5.7. In the case of protein in the 

 milk and the feces the factor used was 6.25. No attempt was made to 

 separate and determine the amount of metabolic nitrogen of the feces. 

 Carefully purified ether was used for determining ether extract in 

 the bread and feces. The results obtained for the fat in the feces 

 were not satisfactory in many cases, although the determinations were 

 made in duplicate by the method generally followed and considered 

 reliable. The fat in the milk was determined by the Adams gravi- 

 metric method. The ash was determined by combustion at a low tem- 

 perature. The carbohydrates were estimated by subtracting the sum 

 of the protein, ether extract, water, and ash from 100. 



The determination of the ether extract in the feces necessarily 

 involves an error, owing to the metabolic products present. Another 

 source of error is in the protein determination. While the determi- 

 nation of the total nitrogen is satisfactory, the factor for converting 

 this nitrogen into protein is not perfectly reliable, and in many cases 

 is very unsatisfactory. It is well known that not all of the nitrogen 

 of a food is in the form of proteid compounds. In the case of the 

 food materials used in these experiments, namely, bread and milk, 

 over 97 per cent of the total nitrogen is in the form of proteids, and 

 the error from nonproteid nitrogen in the food is therefore small. In 

 the case of the feces, however, the kinds, proportions, and composi- 

 tion of the nitrogenous ingredients are not well understood, and the 

 estimate of " protein" is at best very crude. The errors involved in 

 the determination of carbohydrates, by difference, are too well known 

 to require discussion. Notwithstanding these imperfections of analyt- 

 ical methods, which are not peculiar to these investigations l)ut are 

 common to all similar experiments, the results obtained in determining 

 moisture, ash, total nitrogen, and heat of combustion are believed to 

 be reasonably accurate, and the deductions drawn from them are 

 regarded as reliable. 



The calorific value or heat of combustion of the various samples of 

 food, feces, and urine was determined in the usual way by means of 

 the bomb calorimeter. In the case of the milk and urine, weighed 

 blocks of cellulose were employed to absorb the liquid. The absorp- 

 tion block was saturated, carefully dried, weighed, and again satu- 

 rated with a weighed quantity of material. After drying at a tem- 

 perature of 65° C. the block was burned in the calorimeter in the 



