156 PRINCIPLES OF ANIMAL NUTRITION. 
Pentose Carbohydrates.—It has already been shown in Chapter 
II (p. 24) that such of the pentose carbohydrates as have been 
experimented upon are at least partially oxidized in the body, and 
that this appears to be especially the case with herbivora, the urine 
of these animals seldom containing pentoses. 
It is of course conceivable that a substance may be oxidized 
in the body without producing any useful effect except in so 
far as the resulting heat may be of value to the organism, but it 
seems more consonant with our general conceptions of the nature 
of metabolism to suppose that the potential energy of any substance 
which is capable of entering into the metabolism of the cells may be 
utilized as a source of energy for their functions. In the case of the 
pentoses, moreover, we have the additional fact, seemingly well 
established, that~pentoses may give rise, directly or indirectly, to a 
production of glycogen. (Compare p. 26.) If we suppose the 
latter body to be formed directly from the pentoses, then their nutri- 
tive value is established, since that of glycogen is unquestionable. 
If, on the other hand, we suppose that the pentoses enable glycogen 
to be produced by protecting other materials from oxidation, then 
their nutritive value is likewise established, since they serve as a 
source of energy to the organism. 
Recent respiration experiments by Cremer * seem to fully con- 
firm this conclusion. In addition to an only partially successful 
trial with a dog, four experiments were made in which the urinary 
nitrogen and the respiratory carbon of rabbits were determined on 
a diet of varying quantities of rhamnose as compared with a preced- 
ing and succeeding day of fasting. No examination of the feces was 
made, except to determine the amount of rhamnose contained in 
them. Small amounts of this substance. were also found in the 
urine. Neglecting the carbon and nitrogen of the feces and esti- 
mating the urinary carbon from the nitrogen by the use of Rubner’s 
factor,t 0.7462, the following results have been computed, the two 
or three fasting days in each experiment being averaged. The 
amount of rhamnose stated is exclusive of that found in feces and 
urine. 
* Zeit f. Biol., 42, 451. 
+ Ibid., 19, 318. 
