METABOLISM. 29 
§2. Fat Metabolism. 
Scarcely a tissue or portion of the animal body can be named 
in which more or less fat is not found. The muscular fibers, the 
epithelium, the nerves and ganglia, etc., all contain cells in which 
globules of fat may be recognized, so that the capacity to produce 
or store up fat seems to be common to almost all the cells of the 
body. It is particularly in certain cells of the connective tissue, 
however, that the large accumulations of visible fat in the body 
take place. At the outset these cells present no special characters, 
but in a well-nourished animal globules of fat begin to accumulate 
in them, the cells enlarge, the globules of fat coalesce into larger 
ones, and finally the cell substance is reduced to a mere envelope, 
the nucleus being pushed to one side and almost the whole volume 
of the cell occupied by fat. Masses of connective tissue thus loaded 
with fat constitute what is called adipose tissue. Large deposits 
of adipose tissue are met with surrounding various organs, particu- 
larly the kidneys, but the largest deposit of fat is usually in the 
connective tissue underlying the skin. In milk production, too, 
large amounts of fat appear in the epithelial cells of the milk glands. 
Fat Manufactured in the Body.—The older physiologists held 
that all the ingredients of the body pre-existed in the food. Specifi- 
cally, animal fat was regarded as simply vegetable fat which had 
escaped oxidation in the body and been deposited in the tissues. 
But while there is no doubt that the fat of the food can contribute 
to the fat supply of the body, the food of herbivorous animals 
usually contains a relatively small quantity of fat and the amount 
produced by a rapidly fattening animal or by a good dairy cow is 
usually much greater than that consumed in the food. 
Deferring to subsequent pages a discussion of the sources of 
animal fat,* we may content ourselves here with anticipating the 
general results of the great amount of experimental inquiry which 
has been expended upon this question. These results may be 
briefly summarized in the following statements: 
* For avery complete review of the literature of fat production up to 1894, 
see Soskin, Journ. f. Landw., 42, 157. 
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