440 ANIMAL PHYSIOLOGY. 
THE CONSTRUCTION OF Fat, 
It is a well-known fact that, speaking generally, a diet rich 
in carbohydrates favors fat formation, both in man and other 
animals; though it is not to be forgotten that many persons 
seem to be unable to digest such food, or, at all events, to as- 
similate it so as to form fat to any great extent. Persons given 
to excessive fat production are as frequently as not sparing 
users of fat itself. 
It is possible in man and probable in ruminants that fer- 
mentations may occur in the intestines giving rise to fatty acids 
which are possibly converted into fats by the cells of the villi 
or elsewhere. Certain feeding experiments favor the view that 
carbohydrates may be converted into fat or in some way give 
rise to an increase in this substance; for it is to be borne in 
mind that fat may arise from a certain diet in various ways 
other than its direct transformation into this substance itself. 
There are certain facts that make it clear that fat can be 
formed from proteids: 1. A cow will produce more butter than 
can be accounted for by the fat in her food alone. 2. A bitch 
which had been fed on meat produced more fat in her milk 
than could have been derived directly from her food, and this, 
when the animal was gaining in weight, which is usually to 
be traced to the addition of fat; so that the fat of the milk 
was not, in all probability, derived from that of the dog’s 
body; and, as will be seen presently, can. be accounted for 
without such a supposition. 3. It has been shown by analysis 
that 472 parts of fat were deposited in the body of a pig for 
every 100 in its food. 
These facts of themselves suffice to show that fat can be 
formed from proteid, or at least that proteid food can of itself 
give rise to a metabolism, resulting in fat formation; and the 
latter is probably the better way to state the case in the present 
condition of knowledge. 
An examination of the percentage composition of proteid 
and urea renders a possible construction of fat from proteid 
conceivable and in harmony with other better known physi- 
ological facts. 
Carbon. Hydrogen. Nitrogen. Oxygen. Sulphur. 
Probe dicts sitencvee aida 53:00 7:30 15:53 23°04 1:18 
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It will be seen that, if we assume that the urea discharged 
represents the whole of the nitrogen that passes through the 
