278 PRINCIPLES OF ANIMAL. NUTRITION. 
With the exception of the mother’s milk, the results show but a 
slightly greater range than those on the dog. The results of Atwater 
& Benedict,* cited on p. 242, when computed per gram of nitrogen, 
give the following results: : 
Experiment No. 5.............-... 7.055 Cals. 
n Be GL, oe ayaa ayer Gans 7.839 “ 
ry OT abe goes inwcese asap Bs 8.060 “ 
uc pene ree ene ee ee 8.447 “ 
= HO Qe woes apa eee ea 8.3826 “ 
rs NO, cewek Baa 7.575 “ 
The same authors report + the average of 46 determinations as 
7.9 Cals. per gram of nitrogen. Tangl { has reported materially 
higher figures, especially for diets containing large amounts of 
carbohydrates and fat. 
In the case of a mixed diet more or less of the potential energy 
of the feces may be derived from the non-nitrogenous nutrients 
of the food, and we should hardly be justified in making for these 
experiments a computation like that made for the meat diet. The 
rather small range of the figures in most cases, however, would 
seem to show that the metabolizable energy of the proteids of ordi- 
nary mixed dietaries is substantially the same as that found by 
Rubner for carnivora. Tangl’s results perhaps suggest the possi- 
bility of the occasional presence in human urine of non-nitrogenous 
matters similar to those found so abundantly in that of ruminants. 
RvuBNER’s ComPpuTATIONS.—Rubner’s earlier researches did not 
include experiments upon man, but from the results given in the 
foregoing section he endeavored to compute approximate factors 
for the metabolizable energy of the mixed diet of man. For this 
purpose he estimates that, on the average, 60 per cent. of the pro- 
tein of the diet is derived from animal sources and 40 per cent. from 
vegetable. For the animal protein he uses the value found above 
for lean meat, and for vegetable protein the average of the values 
for syntonin and fibrin (since these have an ultimate composition 
* U.S. Dept. Agr., Office of Experiment Stations, Bull. 69. 
+ Report Storrs Expt. Station, 1899, p. 100. 
t Arch. f. (Anat. u.) Physiol., 1899, 261. 
§ Loc. cit., p. 370. 
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