THE FOOD AS A SOURCE OF ENERGY. 285 
Total Organic Matter. 
Coarse Fodders. Frep Atonz.—For Ox H, fed exclusively on 
meadow hay, Kellner obtained the following results * per day and 
head : 
Ingesta. 
7,263 grams meadow hay......... 32,177.3 Cals. 
Excreta. 
2,547 ¢ grams feces....... 11,750.3 Cals. 
13,675 “ —urine....... 1,945.0 “ 
158.4 ‘ methane..... 2,113.7 “ 
Total excreta......................... 15,809.0 “ 
Difference... ...... 0.6... c cece eee 16,368.3 “ 
Had the ration exactly sufficed for the maintenance of the ani- 
mal, the difference of 16,368.3 Cals. would represent exactly its 
metabolizable energy. In reality, however, the nitrogen and car- 
bon balance indicated a gain by the animal of 37.2 grams of protein 
(NX6.00 {) and 140.8 grams of fat, equivalent to 1548.8 Cals., so 
that the amount of energy actually converted into the kinetic form 
was 16,368.3 — 1548.8 = 14,819.5 Cals. The potential energy of the 
140.8 grams of fat, however, while it was not actually rendered 
kinetic, might have been had the needs of the organism required it. 
Its retention in the potential form was, in a sense, temporary and 
accidental, and its energy should properly be considered as a part 
of the metabolizable energy of the food. 
With the gain of protein, however, the case is different. Its 
total potential energy equals 211.2 Cals., but not all of this is 
capable of conversion into kinetic energy. According to Rubner’s 
results (p. 275) each gram of urinary nitrogen derived from the met- 
abolism of the protein of lean meat corresponds to 7.45 Cals. If 
this result is applicable to the forms of protein consumed by her- 
bivora (and we shall see later that there is good reason to believe 
that such is approximately the case), then the metabolism of the 
37.2 grams of protein gained would have added 46.2 Cals. to the 
observed potential energy of the urine, while the remaining 165 
Cals. would have taken the kinetic form and should, therefore, be 
regarded as part of the metabolizable energy of the food. 
; * Loe. cit., 53, 9. + Dry matter. t Compare pp. 67, 68. 
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