THE UTILIZATION OF ENERGY. 455 
The percentages as thus computed are seen to agree fairly well 
with the ones computed for those of Meissl, Strohmer & Lorenz’s 
experiments in which the proportion of protein in the food was 
similar. 
Experiments on Ruminants.—Experiments upon ruminants 
necessarily differ in one important respect from those hitherto con- 
sidered. With carnivora and with swine it is possible to determine 
the fasting metabolism, or, in other words, to trace the line repre- 
senting the net availability or the utilization throughout its entire 
extent. With herbivora, and particularly with ruminants, this is 
practically impossible, for obvious reasons, and the course of the 
lower portion of the line is imaginary. This, however, is no obsta- 
cle to a determination of the net availability or percentage utiliza- 
tion of the food within the limits as to amount prescribed by the 
nature of the animals. As is clear from the graphic discussion of 
the problem on pp. 410 and 446, all that is necessary is to determine 
the gain or loss of energy by the body corresponding to two different 
amounts of food above or below maintenance. A simple com- 
parison of differences then gives in the one case the percentage 
utilization and in the other the net availability of the energy of the 
food added. The method is the same principle as that already 
employed in computing the metabolizable energy of the added 
food. 
THe MéckeRN Exprertments.—The very extensive and elabo- 
rate investigations upon cattle at the Méckern Experiment Station 
by G. Kiibn and Kellner,* which have already been discussed in 
relation to the metabolizable energy of the food, are also our chief 
source of knowledge regarding the utilization of this energy by 
ruminants and will necessarily constitute the principal basis of the 
present discussion. 
These experiments were chiefly upon the fattening of mature 
cattle, various additions being made to basal rations which were 
themselves in almost every case more than sufficient for maintenance. 
The actual gain of carbon and nitrogen by the animals, both on the 
basal and the augmented rations, was accurately determined, and 
from the data thus obtained the gain of proteids and fat and of 
energy was computed in the usual way. By a comparison of the 
* Landw. Vers. Stat., 44, 257; 47,275; 50, 245; 53, 1. 
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