466 PRINCIPLES OF ANIMAL NUTRITION. 
mental results above detailed to be discussed from the standpoint 
of the percentage utilization of the net available energy. 
Furthermore, even confining ourselves to a consideration of the 
utilization of the metabolizable energy of the food, we have already 
seen that the recorded results upon carnivorous animals show such 
, wide divergencies as to render it difficult if not impossible to draw 
any quantitative conclusions from them. 
For the present, accordingly, our discussion of the utilization 
of energy must be confined chiefly to the results which have been 
reached with herbivora, and in the main to the Méckern experi- 
ments, and we must content ourselves with an attempt to trace the 
relations between metabolizable energy and energy utilized, or, to 
look at the subject from the other point of view, with determining 
the proportion of the metabolizable energy of the food which is 
expended in’ the combined work of digestion, assimilation, and 
tissue building. From the practical standpoint this is of course 
the important thing, since either form of expenditure of energy 
constitutes, in the economic aspect of the matter, a waste, but it 
is nevertheless to be regretted that it is at present impossible to 
further analyze this waste. ; 
Influence of Amount of Food.—As in the discussion of net 
availability in Chapter XII, we have thus far assumed the energy 
utilized to be a linear function of the net available or of the metabo- 
lizable energy of the food. Before proceeding further it becomes 
important to consider how far this assumption is justified by the 
facts on record. 
Carnivora.—Of the experiments upon carnivora recorded on 
preceding pages, those of Rubner with different amounts of meat, 
when computed by his method (that is, assuming an availability of 
100 per cent. below the maintenance point, as on p. 450), appear to 
indicate that the utilization above that point is constant. If, how- 
ever, a lower percentage of availability is assumed, as on p. 451, 
this constancy disappears. None of the other results there sum- 
marized seem suitable for discussion from this point of view. 
Swine.—If in the experiments of Meissl, Strohmer & Lorenz, as 
computed on p. 454, we express the estimated metabolizable energy 
of the excess food as a percentage of the fasting metabolism, we 
have the following comparison of the percentage utilization with 
