NET AVAILABLE ENERGY—MAINTENANCE. 433 
and the point K falls above the axis OX will there be an apparent 
exception to this law. In that case, since the energy expended in 
digestion and assimilation seems to be indirectly utilized, the ap- 
parent availability will be 100 per cent. and the metabolizable 
energy required for maintenance will be constant and equal to the 
energy of the fasting metabolism. 
This case might and perhaps does occur with animals whose food 
consumes little energy in digestion, such as the carnivora. As was 
pointed out on p. 412, however, an increase in the work of digestion 
tends to reduce the critical amount of food and there would appear 
to be good reason for believing that, in ruminants at least if not in 
the horse, it lies considerably below the point of maintenance. 
RELATIVE VALUE OF GRAIN AND Coarse FoppER.—We know 
from the investigations of Zuntz & Hagemann (pp. 385-393) that 
the work expended in the digestion of coarse fodders is, in the horse 
and presumably therefore in other animals, materially greater than 
that caused by grain. It follows, then, that a unit of digestible 
matter or of metabolizable energy should have more value for 
maintenance in the latter than in the former. 
That such is the case with cattle is rendered probable by experi- 
ments by the writer.* In the absence of a respiration apparatus 
the nutritive effect of the rations was judged of from the live weight 
and the proteid metabolism during relatively long periods and the 
methane production was computed from the carbohydrates digested. 
A ration in which only about 24 per cent. of the digested organic 
matter was derived from coarse fodder, as compared with rations 
consisting exclusively of coarse fodder, gave the following results 
for the metabolizable energy of the maintenance ration per day 
and 500 kgs. live weight: 
Exclusive coarse fodder, 12 experiments. ... 12,771 Cals. 
Largely grain, 3 experiments.............. 11,023 “ 
Such determinations of the maintenance requirements of the 
horse as have been made tend to confirm the results obtained with 
ruminants. Wolff, in his investigations upon work production 
described in the following chapter, has computed the maintenance 
requirements of the horse in the manner there explained both from 
* Penna. Expt. Station, Bull. 42, p. 159. 
