36 PRINCIPLES OF ANIMAL NUTRITION. 
serves to increase the store of fat in the body depends largely upon 
the total food-supply. When the latter is more than sufficient to 
balance the total metabolism of the organism, the excess may give 
rise to a storage of fat, and under these circumstances the food fat 
or a part of it may, as we have seen, contribute to the increase 
of adipose tissue. On the other hand, when the food-supply is in- 
sufficient, not only is its fat in common with its other ingredients 
in effect consumed to support the vital processes, but the fat pre- 
viously stored in the adipose tissue is drawn upon to make up the 
deficiency. Under these circumstances the fat disappears more or 
less rapidly from the fat cells, passing away gradually either into 
the lymphatics or the blood-vessels in some manner not as yet fully 
understood. 
Fat, then, whether derived immediately from the food or drawn 
in the first instance from the adipose tissue of the body, passes into 
the circulation and serves to supply the demands of the body 
for oxidizable material and energy, the final products of its oxida- 
tion being carbon dioxide and water. Of the intermediate steps 
in this katabolic process we are comparatively ignorant, but one 
hypothesis regarding it has acquired so much importance in its 
bearings on the availability of the potential energy of the food as to 
require mention here. 
Formation OF DExTROSE FROM Fat.—This hypothesis is, in 
brief, that the first step in the katabolism of fat takes place in the 
liver and consists in its conversion into sugar. In other words, it is 
held that the fat of the food or that drawn from the adipose tissue 
of the body supplies the liver with part of the material for its func- 
tion of sugar production described in the previous section. 
This hypothesis is advocated especially by those physiologists 
who, like Seegen in Vienna and Chauveau and his associates in Paris, 
look upon the carbohydrates, and particularly dextrose, as the im- 
mediate source of the energy exerted in muscular contraction or 
in the various other forms of physiological work. The evidence 
upon which this view is based will be considered in subsequent 
chapters. For the present it suffices to point out that, if we admit 
its truth, then the general metabolism of the body is essentially a 
carbohydrate metabolism. Whether we consider the case of a 
fasting animal, living upon its store of protein and fat, or that of an 
