538 PRINCIPLES OF ANIMAL NUTRITION. 
with that of grain, and virtually regards the amount of crude 
fiber as furnishing a convenient empirical measure of the difference. 
In the light of our present knowledge this reserve seems amply 
justified. The difference in the value of coarse fodder and grain 
we should now regard as arising largely from the difference in the 
amounts of energy consumed in digestion and assimilation. Kell- 
ner’s experiments on extracted straw discussed in the previous 
section have shown, however, that with cattle this difference 
is by no means determined by the simple presence of more or less 
crude fiber, but is related rather to the physical properties of the 
feeding-stuff, while Zuntz (see p. 392) has shown that the same 
factor largely affects the work of mastication in the horse. That 
the nutritive value of the rations in Wolff’s experiments was pro- 
portional to the amount of fiber-free nutrients which they contained, 
or, in other words, that the energy expended in digestion, ete., was 
proportional to the digested crude fiber, is explained by the limited 
variety of feeding-stuffs employed. The coarse fodder was meadow 
hay with, in some cases, an addition (usually relatively small) of 
straw, while the grain was commonly oats, part of which was in some 
instances replaced by maize, beans, barley, flaxseed, or oil-meal, 
while starch was added to the ration in a number of trials. The 
larger part of the work of digestion, under these circumstances, was 
probably caused by the coarse fodders, viz., hay and straw, while the 
digested crude fiber was likewise derived chiefly or entirely from 
these substances. Such being the case, it follows that the loss 
of energy through digestive work would be in general proportional 
to the amount of crude fiber in the ration. The essential point in 
Wolff’s experiments is that the omission of crude fiber renders the 
results concordant, and this is as well explained in the manner just 
indicated as by the estimate of Zuntz & Hagemann that the work 
of digesting and assimilating crude fiber consumes the equivalent 
of its metabolizable energy. 
Experiments of 1891-94.—In the dynamometer employed by 
Wolff the resistance was produced by the friction of metallic sur- 
faces. A copy of his dynamometer was employed by Grandeau & 
LeClere in their investigations at Paris, and these experimenters 
found* that the measurement of the work was subject to large errors, 
* Fourth Memoir, p. 49. 
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