24 PRINCIPLES OF ANIMAL NUTRITION. 
the demands of the general metabolism for material to produce heat 
and motion. Plainly, however, the capacity of the muscles and 
the liver to store up carbohydrates is limited, and if the food-supply 
is permanently greater than the demands of the organism, some 
other provision must be made for the excess. Under these circum- 
stances the superfluous dextrose which finds its way into the blood 
gives rise to a production of fat, which is stored up as a reserve in 
special tissues and apparently does not enter again into the general 
metabolism until a permanent deficiericy in the food-supply occurs. 
The experimental evidence of the production of fat from carbo- 
hydrates, as well as the quantitative relations of the process so far as 
they are known, will be considered subsequently. In its relations 
to the economy of the organism the process is analogous to the 
formation of glycogen in the liver, except that the storage capacity 
of the fat tissues is vastly greater, but as compared with the forma- 
tion of glycogen it is distinctively an anabolic process, the fat 
molecule being more complex and containing more potential energy 
than that of dextrose. Hanriot,* assuming the formation of olein, 
stearin, and palmitin in molecular proportions, represents the 
process by the equation: 
13C,H,,0, = CysHyo,0, + 23CO, + 26H,0. 
PENTOSE CARBOHYDRATES. 
The facts of the foregoing paragraphs relate primarily to the 
hexose carbohydrates, particularly starch and sugar, and to a con- 
siderable extent to the metabolism of carnivorous animals. The 
food of herbivora, however, contains a great variety of carbohy- 
drates and especially considerable quantities of the pentose or five- 
carbon carbohydrates. That these substances are in part digest- 
ible, or that at least a considerable proportion of them disappears 
from the food during its transit through the alimentary canal, was 
first shown by Stone,+ and has since been fully confirmed by the 
investigations of Stone & Jones t and of Lindsey & Holland,§ 
but of their further fate in the body relatively little is known. 
* Archives de Physiol., 1893, 248. t Agricultural Science, 5, 6. 
ft Amer. Chem. Jour., 14, 9. § Ibid., 8, 172. 
