280 PRINCIPLES OF ANIMAL NUTRITION. 
was made for the percentage loss in the feces equal to that observed, 
in the actual experiment. The results for the metabolizable energy 
per day were— 
From | C. 4 
Diet. ae ae a 
Cals. 
Potatoes only ........ 0... ccc eee ee ee 1911.4 1911.5 
Rye bread, bolted flour .................. 2060.4 2079.3 
“ ~unbolted flour................ 1773.1 1758.6 
Mixed diet, poor in fat................... 2400.5 2376.0 
BS SCM PON a atte catia Scie ie he eae 2698.8 2600.0 
«0 (ew adatnae {h] el | ag 
Mixed diet—growing boys............ { a oe ears 
As above noted, the computed results include a deduction for 
the energy of the undigested matter in the feces. Rubner finds that 
the heat of combustion of the organic matter of the latter varies 
but little even on extremes of diet, so that the loss through this. 
channel is approximately proportional to the amount of the ex- 
cretion. In the experiments on mixed diet the percentage loss of 
energy in the feces varied from 4.3 per cent. to 7.9 per cent. of 
the energy of the food. 
ATWATER’S INVESTIGATIONS.—By far the most extensive data 
as to the metabolizable energy of human foods and dietaries are 
those derived from the investigations upon human nutrition made 
under Atwater’s direction by the United States Department of 
Agriculture with the codperation of Wesleyan University, the 
Storrs Experiment Station, and various other experiment sta- 
tions. Atwater & Bryant* have summarized these results in a 
preliminary report of which the essential features are given in 
the following paragraphs. 
From the best data available, the heats of combustion of the 
protein, carbohydrates, and fats of various classes of foods are esti- 
mated. In these estimates account is taken as fully as possible of 
the proportion of nitrogen in proteid and non-proteid forms, and 
of the varying percentage of nitrogen in different proteids, the nitro- 
gen factors used being those quoted on p. 6. The accuracy of 
* Report Storrs Agr. Expt Station, 1899, p. 73. 
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