THE UTILIZATION OF ENERGY. 473 
principal classes of nutrients rather than commercial feeding-stuffs. 
Accordingly such representative materials as starch, oil, and glu- 
ten were largely used, and we have as yet but few determinations 
either of the metabolizable energy of ordinary concentrated feeding- 
stuffs or of its percentage utilization. We have already considered 
to some extent the advantages and disadvantages resulting from 
making the pure nutrients, on the one hand, or actual feeding-stuffs, 
on the other, the starting-point for investigations. Passing over 
this question for the present, we may conveniently group together 
here such results as are on record for materials other than coarse 
fodders. 
Starch.—Starch, as a representative of the readily digested car- 
bohydrates, has, as we have seen, received a large share of atten- 
tion. The results obtained are tabulated in the Appendix, and 
have already been partially considered in their bearings upon the 
influence of amount of food. It was there noted that the earlier 
series of experiments by Kiihn, in which the starch was added to 
a ration of coarse fodder only, gave results differing decidedly from 
those obtained later by Kellner from the addition of starch to a 
mixed fattening ration. Among the latter experiments, more- 
over, were two (animals B and C) which were exceptional in that 
very large total amounts of starch were contained in the ration, 
relatively large amounts escaping digestion, while none of the added 
starch underwent the methane fermentation. 
A clear image of the fate of the total potential energy supplied 
to the organism in the starch is best obtained by a study of its per- 
centage distribution among the several excreta, the work of digestion, 
assimilation, and tissue building, and the gain secured, as in the 
table on page 474, in which each of the three sets of experiments 
indicated above is given separately. The figures for the work of 
digestion, etc., are, of course, obtained by difference. 
As pointed out in the discussion of metabolizable energy, the 
percentage of the gross energy carried off in the feces includes, as 
here computed, not only the energy of the undigested portion of the 
starch itself, but also that of the portion of the basal ration which 
escaped digestion under the influence of the starch. This is espe- 
cially true of Kellner’s experiments with moderate rations, in which 
little or no starch could be detected in the feces. Similarly, the 
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