74 VITALITY AND EFFICIENCY WITH RESTRICTED DIET. 



FOODS AND FECES. 



The dried samples of foods and feces were analyzed for total nitrogen 

 by the Kjeldahl process. Here again the nitrogen content of samples 

 a and h supplied a check upon each other. 



HEAT OF COMBUSTION. 



To obtain an energy balance, it was necessary that we should find 

 the actual calories in the intake of food. Of the output it was possible 

 for us to determine only the calories in the feces. Since, however, 

 there are reasonably constant standard factors for computing the calo- 

 ries from the percentage of nitrogen in urine, we resorted to this method 

 rather than attempt to dry down the 1,000 or more samples of urine 

 obtained in the research and determine the heats of combustion with 

 the bomb calorimeter. The daily output of energy in urine was found 

 by multiplying the total number of grams of nitrogen by the factor 8.0. 

 The energy as thus calculated was almost invariably somewhat under 

 100 calories, so that the error due to the method cannot at best be an 

 appreciable portion of the total energy under consideration for the day. 



The heats of combustion of the feces and dried foods were determined 

 with a bomb calorimeter of the Kroker type in an adiabatic calorimeter. 

 This calorimeter was developed in the Nutrition Laboratory and pro- 

 motes rapid operation.^ The technique was finally so adjusted that 

 after the various dried pellets of feces and food had been prepared and 

 weighed and placed in nickel capsules. Miss M. A. Corson and her 

 assistant were able to determine and compute four heats of combustion 

 per hour. This made it possible to complete this extensive series of 

 determinations within a reasonable time. 



Since the total nitrogen and calories were obtained, it was deemed 

 unnecessary to make an exact apportionment of the energy of the intake 

 between protein on the one hand and fat and carbohydrate on the 

 other. It is perfectly possible, knowing the total caloric value and 

 nitrogen of the intake, to compute the calories due to protein. The 

 remainder will be due to fat and carbohydrate. These were all mixed 

 diets, with no special dietary adjustments other than decrease in the 

 portions served. It hardly seemed advantageous to determine the 

 fat in the food intake; indeed, the time requirement for such determi- 

 nation for all of the samples would alone preclude this additional work. 

 A few special fat extractions were made which will be mentioned in the 

 text from time to time, but there was nothing to indicate that exact 

 information regarding the relative proportion of calories from fat and 

 carbohydrate would have a special significance in the discussion of the 

 results. 



1 Benedict and Higgins, Journ. Am. Chem. Soc, 1910, 32, p. 461. 



