INTERNAL WORK. 389 
proportion of crude fiber in the hay ration. Ascribing the differ- 
ence in digestive work entirely to the crude fiber, the authors en- 
deavor to estimate the expenditure of energy on this ingredient 
as follows: ‘ 
Digestive Work FoR CrupE Fisrer.—The hay ration con- 
tained 1572 grams less of (estimated) digestible matter and 648 
grams more of total crude fiber than the mixed ration. The com- 
puted evolution of energy per head for the twenty-four hours was 
greater by 772 Cals. in the hay period. On the basis of Magnus- 
Levy’s results the authors assume that the expenditure of energy 
in the digestion of the nutrients exclusive of crude fiber equals 9 
per cent. of the total energy of the digested matter. For 1572 
grams (fat being reduced to its starch equivalent) this amounts to 
4.1X1572X0.09=580 Cals. Accordingly, the energy metabo- 
lism should have been 580 Cals. less in Period ¢ than in Period f. 
It was actually 772 Cals. greater, a difference of 1352 Cals. This 
difference is ascribed to the presence of the 648 grams more of total 
crude fiber, and corresponds to 2.086 Cals. per gram. With an 
average digestibility of 55 per cent. this would equal 3.793 Cals. 
per gram of digested crude fiber, an amount slightly exceeding its 
metabolizable energy as computed on p. 331. In other words, it 
would appear that all the metabolizable energy of the crude fiber 
(or even more, should the digestibility fall below the percentage 
assumed) is consumed in the work of digestion and converted into 
heat, leaving none available for external work, and this result seems 
to coincide strikingly with the results obtained by Wolff * by an 
entirely different method. (Compare Chapter XIII, § 2.) 
It is to be observed, however, that the basis of Zuntz & Hage- 
mann’s computation is the difference between the energy required 
for the digestion of the 648 grams of crude fiber and that required 
for the digestion of an equal amount of fiber-free nutrients. To 
get at the total expenditure upon the digestion of the crude fiber 
we should make the following computation: 
The nutrients other than crude fiber digested were in Period f 
5124 grams and in Period c 2608 grams, a difference of 2516 grams. 
The corresponding difference in the work of digestion would, on the 
* Grundlagen, etc., Neue Beitrige, 1887, p. 94. 
