THE FOOD AS A SOURCE OF ENERGY. 323 
non-nitrogenous matter of the food. It is clear, then, that the 
non-nitrogenous moiety of the hippuric acid and the non-nitrogen- 
ous organic matter of the urine together represent a large share 
of the potential energy of the latter, and that it is quite as in- 
correct to compute the metabolizable energy of the protein on the 
assumption that all the energy of the urine is derived from it as it 
is, on the other hand, to simply deduct from its gross energy the 
energy of the equivalent amount of urea. 
Ether Extract.—Our only data upon this ingredient are fur- 
nished by the four experiments upon steers by Kellner in which 
peanut oil was added to the ration. In the first two experiments 
this oil was emulsified by means of a small quantity of soap made 
from the same oil. The result was a milky fluid which was readily 
digestible and which caused no considerable decrease in the digesti- 
bility of the basal ration. In the second two experiments the oil 
was emulsified with lime-water, giving a thickish mass which was 
not very well digested and which, in the case of Ox F particularly, 
caused a considerable decrease in the digestibility of the crude fiber 
and nitrogen-free extract of the basal ration. It should be noted 
that in the experiment with Ox E the oil was not added to a basal 
ration, but was substituted for a part of the bran. From Table VI 
of the Appendix we obtain the summary tabulated on the next 
page, showing the effects of the oil upon the loss of energy in the 
gaseous hydrocarbons and in the urine, the results of the experi- 
ment on Ox E being included. 
Upon the evidence of these four experiments, bearing in mind 
that the one with Ox E was upon the substitution of oil for bran, 
we should not be inclined to ascribe to the fat of the food any con- 
siderable effect either upon the formation of hydrocarbons or upon 
the amount of potential energy carried off in the urine. As regards 
the hydrocarbons, the differences in the cases of Oxen D and G are 
insignificant. In the case of Ox F, on the contrary, the production 
of hydrocarbons was reduced nearly one half; this it may be noted 
was the case in which there was a considerable effect upon the 
digestibility of the basal ration. As regards the energy of the urine, 
the differences, except in the case of Ox E, are relatively small and 
are in both directions. 
Provisionally, therefore, we are probably justified in assuming 
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