19 



ciliated, as in former work, l\y assiiminjj that 1>7 per cent of the pro- 

 tein, 95 per cent of the fat. and 1>S per cent of the carbohydrates of 

 the milk were digested. These values have l)een deduced from the 

 results of a lai'ge numt)erof digestion ex])erinients with l)oth ordinar}' 

 and special diets." The undigested luitrients of the milk, as calcu- 

 lated bv the use of these factors, subtracted from the total nutrients 

 in the feces j^ive the estimated undig-ested nutrients from bread, and 

 these subtracted from the total nutrients of the bread give the digesti- 

 ble nutrients in bread. These last divided by the total nutrients in 

 the bread and nudtiplied by 100 give the percentages or coetticients of 

 digestibility of bread alone. 



The amounts of energy given for the l)read and milk and the total 

 feces were determined ])y multiplying' the total weight of each mate- 

 rial b}' its heat of combustion as determined with the bomb calorimeter. 

 The proportion of energy in total food estimated to be available to the 

 bod}^ was found by dividing the energv of the total digested food by 

 the energy of the total food. 



In order to estimate the amounts of energy in the feces from bread 

 alone, the energv of the feces from food other than bread (in this case 

 milk) was computed by means of factors. Previous investigations'' 

 have shown that the heat of combustion of the nutrients in dairy prod- 

 ucts are, per gram, as follows: For protein, 5.65 calories; for fat, 9.25 

 calories; and for carV)ohydrates, 3. 9 calories. By multiplying the weights 

 of the nutrients in the feces from food other than bread by these factors 

 and adding the products an estimated enerj^y value is obtained. It is 

 known, however, as pointed out on page 13, that the energy of food 

 materials, when estimated by the use of factors, varies somewhat from 

 the value obtained by actual combustion in the bomb calorimeter. A 

 similar variation is found in the total feces, and undoubtedly would be 

 found in the feces from a portion of the diet could a separation be 

 ejected and the actual heat of combustion determined. In order to 

 approximate this latter value as closely as possible, the energy of the 

 total feces was also calculated by means of factors. In this case, how- 

 ever, since the total feces were made up of the residues from two 

 foods — milk and bread — the factors used were those computed * for a 

 mixed diet, these values being per gram as follows: Protein, 5.65 calo- 

 ries; fat, 9.1: calories, and carbohvdrates, 1.15 calories. It was then 

 assumed that the diti'erence in values existing between the energy of 

 the total feces as thus computed and as actually determined is propor- 

 tional to the presumed difference in value between the energy of the 

 feces from food other than bread as computed and the value which 

 would be obtained could an actual determination be made. In other 

 words, the calculated energy of the total feces is to the determined 



o Connecticut Storrs Station Rpt. 1899, pp. 84-86. 

 b Connecticut Storrs Station Rpt. 1899, p. 104. 



