THE FOOD AS A SOURCE OF ENERGY. 293 
of the organic matter is 2.977 Cals. per gram. This would be a mini- 
mum figure, while if we assume, as suggested above, that the mo- 
lasses is entirely digestible, this figure is still too low and should be 
increased to equal the gross energy of the organic matter. 
If, however, either one of these latter values were used in com- 
puting the metabolizable energy of rations, the results would obvi- 
ously be too high unless corrections were made for the effect upon 
the apparent digestibility of the other feeding-stuffs in the ration. 
The figure first computed, while including several different effects, 
nevertheless seems better adapted for use in actual computations 
under average conditions, while the second gives the more accurate 
idea of the store of metabolizable energy contained in the feeding- 
stuff regarded by itself. The distinction is analogous to that 
between apparent and real digestibility, and we may accordingly 
speak of the apparent and the real metabolizable energy of feeding- 
stuffs. 
The whole of our present discussion of the metabolizable 
energy of the organic matter (total or digestible) of food materials 
relates to the apparent metabolizable energy. This is obvious as 
regards the concentrated feeds from the above example, and logic- 
ally applies also to those cases in which coarse fodders were added 
to the basal ration, while in the case of the coarse fodders used alone 
the distinction vanishes or is reduced to one between apparent and 
real digestibility. The experiment with beet molasses well illus- 
trates the difficulties in the way of determining the actual metabo- 
lizable energy of feeding-stuffs which cannot be used alone. 
Breet Mo.asses.—In two later experiments the addition of 
molasses increased instead of diminishing the excretion of methane. 
The results of the three experiments upon molasses, computed in 
the same manner as the experiments upon coarse fodders, are con- 
tained in Table II of the Appendix. 
In the last two experiments 10 to 12 per cent. of the energy of 
the molasses was lost in the products of intestinal fermentation, 
but this was more than counterbalanced by its less effect upon the 
digestibility of the rations, so that the final result is a higher figure 
for the apparently metabolizable energy thanin the first experi- 
ment. Summarizing the results per gram as in the case of the 
coarse fodders we have: 
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