494 | PRINCIPLES OF ANIMAL NUTRITION. ° 
inclined to explain by its well-known effect in stimulating the met- 
abolism in the body—that is, by supposing that for this substance 
our assumption of 30 per cent. for the work of assimilation and 
tissue building is too low. 
The computed work of digestion is small in the case of the oil, 
as the results obtained in other experiments would lead us to expect. 
At the same time it should be remembered that the figures given 
are derived from two experiments only, while a third gave quite 
different results, showing in particular a decidedly higher figure for 
the combined work of digestion, assimilation, and tissue building. 
It is obvious, therefore, that further investigation is necessary to 
fix the value of oil in this respect. 
CrupE Fisper.—Finally, it will be observed that our arbitrary 
assumption results in making the work of digestion of the extracted 
straw less than two thirds that of starch. We should naturally 
suppose that the mechanical work involved in digestion would be 
fully as great in the case of the former as-in that of the latter, while, 
as the figures for methane show, the extracted straw underwent a 
more extensive fermentation than the starch. Obviously, the 
mechanical and chemical treatment to which the straw was sub- 
jected so modified the cellulose and removed incrusting matters as 
to produce a material which behaved substantially like starch in the 
alimentary canal, both as regards its digestibility and its relation to 
ferments.* Correspondingly, the total work of digestion, assimila- 
tion, and tissue building is not widely different in the two cases. It 
is only when we arbitrarily assume a high percentage for the work of 
assimilation and tissue building, as was done above for the sake of 
illustrating the general question, that this difference and that in the 
amount of metabolizable energy combine to give the relatively low 
figure for digestive work noted above. 
§ 2. Utilization for Muscular Work. 
When a muscle is subjected to a suitable stimulus (normally a 
nerve stimulus) there occurs, as we have seen, a sudden and rapid 
increase in its metabolism. .This increased metabolism appears to 
* Lehmann (Landw. Jahrb., 24, Supp. I, 118) had previously shown that 
the apparent digestibility of the crude fiber and nitrogen-free extract of straw 
and chaff thus treated was increased by from 79 to 133 per cent. 
