THE UTILIZATION OF ENERGY. 457 
discussion of the metabolizable energy of feeding-stuffs, the un- 
avoidable slight variations in the moisture-content of the latter 
in the Méckern experiments resulted in slight differences in the 
amounts of organic matter of the basal ration consumed in the 
several periods. A comparison, then, between two periods, as re- 
gards metabolizable energy and resulting gain, shows the effect of 
the added feeding-stuff plus the effect of this small difference. 
For the metabolizable energy an approximate correction was com- 
puted. In order to make a similar correction in the resulting gain 
of tissue, however, it is necessary to know to what extent this 
difference in metabolizable energy contributed to the observed 
gain; that is, to know the percentage utilization of the basal ration. 
No direct determinations of this factor, however—that is, no com- 
parisons of the results of feeding different amounts of the basal 
ration—were made. In his discussion of the results Kellner virtually 
assumes a percentage of utilization by subtracting from the total 
metabolizable energy of the food the average amount required for 
maintenance as determined by his own experiments and then com- 
paring the energy in excess of the maintenance requirement with 
the resulting gain. 
Differences in Live Weight.—The live weights of the animals in 
the Moéckern experiments differed considerably in the different 
periods. This would probably result in differences in the require- 
ments for maintenance, although the data at hand seem insufficient 
to satisfactorily determine the relation between live weight and 
maintenance (see p. 441). Kellner assumes that the maintenance 
ration is in proportion to the two-third power of the live weight, a 
result which has already been shown to correspond fairly well with 
the results upon Ox B, although in apparent conflict with the aver- 
age results obtained on other animals. 
Utilization of Basal Ration.—In order to be able to correct the 
results for differences in organic matter consumed and differences 
in live weight, it is necessary, as has just been pointed out, to know 
the percentage utilization of the basal ration. This Kellner assumes 
in assuming a maintenance ration. There are, however, serious ob- 
jections to this method of procedure. First, the maintenance ration 
used by Kellner is an average, based on results which were obtained 
with a number of animals, not including all those used in the fatten- 
