to the liver as a necessary preliminary to its
metabolism. 10% of the fat, i.e., the gly-
cerine fiaction, we may consider as being con-
rerted into glucose, the remaining 90%, the
fatty acid fraction, is prepared for tissue uses
and is sent out to the tissues to be finally dis-
posed of.
The carbohydrate of the food is by the diges-
tive process converted into sugar, glucose in
the main, and absorbed into the portal blood as
such. The sugar which thus enters the blood
stream may, as in the case of fat, be either
temporarily put in storage or it may suffer im-
mediate oxidation. By far the larger part of
the absorbed sugar is temporarily stored in the
form of animal starch or glycogen in the liver
and muscles. The intermediary metabolism of
glucose is not definitely understood but it
wroold appear that in the normal animal, glu-
cose is oxidized very readily to C02 and H20
and may be looked upon as tinder in the proto-
plasmic fires in contrast to the hard coal or fat
in the same. It is possible to have a certain
fraction of the ingested carbohydrate con-
verted into fat and stored as such in the
organism.
For practical purposes it is best to consider
the three food principles as resolvable into two
fractions, one sugar, the other fatty acid. We
express this mathematically when we say that
58%° of the protein, 10%o of the fat and
00%o of the carbohydrate is to be considered
as so much potential glucose, and 46% of the
protein and 90%o of the fat as so much poten-
tial fatty acid.
As pointed out before, glucose is so readily
bulirned in the protoplasmic fires of the normal
animal that it has been likened to a tinder fuel
while fatty acid, which is much higher in
fuel value than sugar and is burned with
greater difficulty has accordingly been likened
to a hard coal fuel. The statement has fre-
quently been made that the fatty acids are
6