Nitrogen Metabolism Experiments. 275 



At the conclusion of the food experiment inside the chamber, which 

 usually lasted 3 days, the subject came out of the respiration apparatus, and 

 resumed his customary dietetic habits. After metabolism experiment No. 76, 

 the subject began the experiment outside the chamber, the results of which are 

 here recorded under the convenient heading of Nitrogen Metabolism Experi- 

 ment No. 1. The second nitrogen metabolism experiment immediately followed 

 metabolism experiment No. 77. 



The peculiar dietetic habits of the subject of these experiments resulted 

 in his selecting a very extended list of food materials. He was left perfectly 

 free to choose whatever he wished both as to kinds and amounts of food. 

 In general, meat was partaken of very sparingly. Milk, fruit, cereals, and 

 eggs, together with peanut butter, were the chief articles of diet. 



The wide variety of food selected may be seen from table 175, which gives 

 the percentage composition and the different kinds of food used in both nitrogen 

 metabolism experiments. The values here recorded are used in subsequent 

 computations to test the accuracy of the method of sampling the food employed 

 in these experiments. 



The percentage composition of the foods given in this table is taken for the 

 most part from the compilation of analyses of American food materials 

 published by Atwater and Bryant. 83 In many instances the analyses taken from 

 the bulletin referred to, were revised by averaging with new unpublished data. 



Sampling and Analysis. 



It was impracticable to sample and analyze each kind of food consumed 

 each day. The following plan was therefore adopted: The amount of each 

 kind of food eaten in a given 24 hours was determined, and a tenth of each kind 

 of food was placed in a dish. These different samples formed, then, a com- 

 posite representing one-tenth of all the food eaten and including each kind of 

 food. This composite sample was dried in the water oven, then weighed, 

 mixed and ground preparatory to its analysis. Determinations were made 

 on the sample for each day, of nitrogen, phosphorus, sulphur, and the heat 

 of combustion. 



Calculated amounts of protein and energy of food. The method of sampling 

 and analysis outlined above is open to the objection that one or more articles 

 of so varied a diet might be overlooked in preparing the daily composite 

 samples. As a partial check on the accuracy of this method of sampling, the 

 amounts of protein and energy in the food consumed per day have been 

 computed from the weights of the different foods eaten and the percentage 

 composition given in table 175. This table is furthermore of interest in 

 showing the kinds and amounts of food eaten each day. 



33 U. S. Dept. Agr., Office of Expt. Sta. Bui. 28 (1898). 



