38 



Table 17. — Composition of water-free feces in digestion experiments with Maine 



lumbermen. 



Lab- 

 ora- 

 tory 

 No. 



67tJ5 

 67tK) 

 67(5" 



%m) 



6801 

 6803 



Feces. 



Experiment No. 463 

 Experiment No. 4(i4 

 Experiment No. 46.5 

 Experiment No. 466 

 Experiment No. 467 

 Experiment No. 468 



Heat of 

 combus- 

 tion per 

 gram. 



Calories. 

 5.357 

 5.351 

 5.367 

 5. .503 

 5.284 

 5.382 



DETAILS OF DIGESTION EXPERIMENTS. 



The details of the digestion experiments are included in Tables 

 18-23. These show the kinds and amounts of food eaten by the 

 subject. The quantities in the column "total organic matter" are 

 the sums of the quantities in the three following columns, "protein," 

 "fat," and "carbohj^drates." The amounts of protein, fat, and car- 

 bohj^drates in each food material and in tlie feces were computed from 

 the weight of each material multiplied by its percentage composi- 

 tion and heat of combustion, as shown in Table 16. For conve- 

 nience the same reference numbers for the food materials and feces 

 are used in the tables of composition and in the tables giving the 

 weights of nutrients in the foods. The differences between the total 

 nitrogen of the food eaten and that rejected in the feces are taken as 

 a measure of the total amount digested. The feces, however, do not 

 consist solely of undigested residue, but contain a large amount of 

 metabolic products. The amount of metabolic nitrogen in tlie feces, 

 as found by two different methods, is given in Table 24 and discussed 

 on page 55. The amounts of nutrients rejected in the feces, while 

 not strictly representing the undigested parts of the food, do repre- 

 sent approximatelj^ the amounts which were not available to tlie body. 

 The point has been discussed at length by Atwater.« The total amount 

 of any particular kind of nutrient digested divided by the total amount 

 of this nutrient in the food gives the percentage which is digestible 

 or actually available to the body. These percentage values are called 

 coefficients of digestibility. These coefficients are given in the last 

 line of each of the tables showing the details of the digestion experi- 

 ments and are summarized in the table on page 52. 



While the coefficients of digestibility of the different nutrients repre- 

 sent the iiroportion which the body actually utilizes, the corresponding 

 value for the heat of combustion of the food does not represent the actual 

 amount of energy which the body obtains from the food absorbed from 

 the alimentary canal. When protein is burned in the bomb calorimeter 

 the carbon is oxidized to carbon dioxid and the hydrogen to water. 

 The nitrogen is left in the free state. When protein is burned in the 



"Connecticut Storrs Station Rpts. 1896 and 1897. 



