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The Vitamine Manual by Walter H. Eddy
page 11 of 168 (06%)

We had reached this status some time before 1911. But, a short time before
this, there had arisen a controversy as to the relative value of different
types of proteins. The animal- vs. vegetable-protein controversy was one
of the side shows of this affair. This controversy had led to a careful
study of the different kinds of proteins that are found in foodstuffs.
Through a brilliant series of chemical investigations for whose
description we haven't time or space here, chemists had shown that every
protein was built up of a collection of acids which were different in
structure and properties, that there were some seventeen of these in all
and that any given protein might have present all seventeen or be lacking
in one or more and that the proportions present varied for every type of
protein. It was then obvious that proteins could not be considered as
identities. More than that, it was the necessary task of the food expert
to separate all proteins into their acids or building stones and not only
show what was present and how much but determine the role each played in
the body. To this task many set their faces and hands.

From the results there has accrued much progress in the evaluation of
proteins but an unexpected development was the part played by these
investigations in the story of the vitamines.

About 1909-1910 Professors Osborne and Mendel under a grant from the
Carnegie Institution began a detailed investigation into the value of
purified proteins from various sources. In their experiments they used the
white rat as the experimental animal and proceeded to feed these animals a
mixture consisting of a single purified protein supplemented with the
proper proportions of fat carbohydrate, and mineral salts. Since the food
furnished was composed of pure nutrients and always in excess of the
appetite of the rat the necessary number of calories was also present.
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