THE FOOD AS A SOURCE OF ENERGY. 315 
Other Species —We may probably assume without serious error 
that the results obtained with cattle apply in general to sheep and 
other ruminants. No direct determinations of the energy of the 
urine of the horse or the hog have yet been reported, but Zuntz & 
Hagemann * have made some estimates of it in the case of the 
horse on a mixed ration of hay, oats, and straw. They determined 
the total carbon and total nitrogen of the urine and, on the assump- 
tion that only urea and hippuric acid are present, compute the 
proportion of each of these, and thence jhe energy of the urine. 
They thus find the potential energy of the latter, per gram of nitro- 
gen, equal to 15.521 Cals. Neither hippuric acid nor energy having 
been determined directly, it is impossible to check the above com- 
putation or to ascertain whether any non-nitrogenous organic 
matter was present. It is to be noted, however, that the ratio of 
carbon to nitrogen in the urine was much lower than in Kellner’s 
experiments on cattle, viz.: 
Zuntz & Hagemann................ 1.526 :1 
Kellner, Ox A....... cee cece eee 3.315 21 
OX: Beas waves oaks eee eee 3.458 : 1 
This fact clearly indicates that at least there was very much less 
non-nitrogenous matter present in the former case. 
Meissl, Strohmer & Lorenz { in their respiration experiments 
on swine likewise determined carbon and nitrogen in the urine. 
Computed by the method of Zuntz & Hagemann the energy of the 
urine averaged 9.55 Cals. per gram of nitrogen, while the average 
ratio of carbon to nitrogen was 0.745 :1. These results would 
seem to indicate that the loss of energy in the urine of the hog 
is not very much greater than in that of the carnivora. 
METABOLIZABLE ENERGY OF PROTEIN OF CONCENTRATED FEEDS. 
—Accepting it as demonstrated that there is no material loss of 
potential energy in the form of fermentation products of protein, 
the data regarding the energy of the urine just considered afford 
the basis for an approximate estimate of the metabolizable energy 
of the digested protein. 
Catile.—Kellner’s experiments upon cattle afford data for com- 
puting the metabolizable energy of the digested protein of wheat 
* Landw. Jahrb., 27, Supp. ITI, 239. ft Zeit. f. Biol., 22, 63. 
