26 PRINCIPLES OF ANIMAL NUTRITION. 
glycosuria caused by large doses of the common sugars. The pen- 
tose carbohydrates in the ordinary food of herbivora, however, are 
largely or entirely the comparatively insoluble pentosans. As 
already stated, these bodies are partially digested—that is, they do 
not reappear in the feces. As to the manner of their digestion we 
are ignorant. If we are justified in assuming that the digested 
portion is converted, wholly or partially, into pentoses, then the 
conditions differ from those of the experiments above mentioned 
in that the production and assimilation of the pentoses is gradual. 
Under these circumstances we might be justified in anticipating 
a more complete oxidation of these bodies. To what extent this 
is true it is at present impossible to say. Weiske,* in connection 
with his investigations upon the digestibility of the pentosans, states 
that the urine of the sheep and rabbits experimented upon gave 
only a slight reaction for pentoses. The writer has not been able 
to find any records of other tests of the urine of domestic animals 
for pentoses. 
PENTOSES AS A SOURCE OF GLycoGEN.—Most, although not 
all, investigators have found an increase in the glycogen of the liver 
consequent upon the ingestion of pentoses, but in every case it has 
been the ordinary six-carbon glycogen. This has been commonly 
and most naturally interpreted as showing that the pentoses are not 
themselves converted into glycogen in the body, but are simply 
oxidized in-the place of some other material which is the true source 
of the observed gain of glycogen. In the light of known facts 
regarding the apparent power of the liver to produce glycogen from 
very diverse hexoses (see p. 20) it would seem, however, that the 
possibility of an actual assimilation of the pentoses by the hepatic 
cells should at least be borne in mind. 
THE ORGANIC ACIDS. 
Tn addition to such quantities of the organic acids, free and com- 
bined, as are contained in their food, relatively large amounts of 
these substances are, in the case of herbivorous animals and par- 
ticularly of ruminants, produced by the fermentation of the carbo- 
hydrates in the alimentary canal. For this reason their meta- 
* Zeit. physiol. Chem., 20, 489. 
