THE FOOD AS A SOURCE OF ENERGY. 331 
mann & Zuntz * in eight respiration experiments obtained the 
following results, the hydrocarbons being computed as methane: 
Crude Fiber Digested. Methane Excreted. 
698 .5 grams 26.8 grams 
5388.9 33.4 “ 
451.7 “ . 12.0 “ 
“ce 6c 20.0 ce 
iz¢ “c 16.4 iz3 
ce “cc 31 .0 (<3 
“ if3 22 : 1 (z3 
(z3 cc 23 .0 “cl 
As already noted on p. 326, Zuntz + has pointed out that the 
fermentation of the food in the horse takes place largely in the 
ccecum and after the more digestible carbohydrates have been 
resorbed. The authors consequently compute the excretion of 
methane entirely upon thé crude fiber of the food. On the average 
of the eight somewhat discordant experiments, in which the food 
consisted of oats, hay, and cut straw, 100 grams of digested crude 
fiber yielded 4.7 grams of methane, which corresponds exactly with 
the results reported by Tappeiner { for the artificial fermenta- 
tion of cellulose. In the same experiments an excretion of approxi- 
mately 0.203 gram of hydrogen per 100 grams digested crude fiber 
was observed. Deducting the corresponding amounts of energy 
from the energy of the apparently digested cellulose we have— 
Total energy of 1 gram.. : 4.220 Cals. 
Energy of CH, (0.047 pratt, 0. 627 Cal. 
Energy of H (0.002 gram)... 0.070 “ 0.697 Cal. 
Metabolizable energy of 1 gram............. 3.523 Cals.§ 
While less methane is apparently produced by the horse than 
by the ox, the assumption that it all arises from the fermentation 
of the crude fiber gives the latter a metabolizable energy not greatly 
different from that found in the case of the ox. It is of course 
* Landw. Jahrb., 238, 125. 
+ Arch. ges. Physiol., 49, 477. 
t Zeit. f. Biol., 20, 88. 
g As computed by the authors, 3.487 Cals. on the basis of 4.185 Cals. 
total energy per gram of crude fiber. 
