THE FOOD. 11 
used chiefly in connection with human nutrition. In discussions of 
animal nutrition the terms digestible and digestibility have become 
so firmly established that it may be questioned whether the intro- 
duction now of a new term would not create more confusion than it 
would prevent, and whether it is not preferable, when strict accuracy 
of expression is required, to attach a modifying word and designate 
the difference between food and feces as apparently digestible, in 
distinction from the real digestibility, which we cannot as yet deter- 
mine. 
DETERMINATION OF APPARENT DIGESTIBILITY.—The determi- 
nation of the apparent digestibility of the nutrients of a feeding- 
stuff in the above sense, or of their “ digestibility ” in the older sense, 
consists simply in determining the amount of the feces or of their 
separate ingredients and comparing them with the correspond- 
ing amounts in the food. . 
Aside from ordinary analytical precautions, the chief condition 
of accurate results is that the feces correspond to the food consumed. 
In animals with a comparatively simple digestive canal, like man 
and the carnivora, this is readily brought about by the ingestion of 
a small amount of some substance like powdered charcoal or infu- 
sorial earth, which is in itself indigestible and which serves to sepa- 
rate the feces of two successive periods. In the case of herbivora, 
on the other hand, the undigested residues of the food become mixed 
to a large extent with those of the previous period. In this case, 
therefore, it is essential that a preliminary feeding be continued for 
a sufficient length of time to remove the residues of previous foods 
from the digestive organs, and further that the experiment itself 
extend through a number of days in order to eliminate the 
influence of irregularity of excretion. 
SIGNIFICANCE OF Rusutts.—It is plain from what has just 
been said that what the results of such an experiment actually 
show is that a certain amount of material has disappeared from 
the food during its transit through the alimentary canal. This 
fact of itself. however, does not necessarily show that the missing 
material has been digested in any true sense. In the case of animals 
possessing a relatively short, and simple digestive apparatus. we are 
probably justified in assuming that the difference between food and 
undigested matter represents material that has actually been 
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