combination with the alcohol-ether extracted diet amounts of purified fats
corresponding to what was removed by the alcohol-ether. The results were
totally unexpected for _none_ of the purified fats substituted were
adequate to secure growth! When, however, he evaporated off his alcohol-
ether from the extract of the bread and milk and returned that residue to
the diet, growth was resumed as before. The conclusion was obvious, viz.,
that alcohol-ether takes out of a mixture of bread and milk some factor
that is necessary to growth and that factor is not fat but something
removed by the extraction with the fat. These results led Stepp to suspect
the existence of an unidentified factor but he was unable to identify it
as a lipoid. He makes the following statement which is now significant:
"It is not impossible that the unknown substance indispensable to life
goes into solution in the fats and that the latter thereby become what may
be termed carriers for these substances." These studies were published
between the years 1909 and 1912 and were therefore concurrent with those
of Funk and Osborne and Mendel.

But there was still another set of studies that led up to this vitamine
work. In 1907 E. V. McCollum began the study of nutrition problems at the
Wisconsin Experiment Station. At the time he was especially interested in
two papers that had been published just previous to his entrance into the
problem. One of these papers by Henriques and Hansen told how the authors
had attempted to nourish animals whose growth was already complete on a
mixture consisting of purified gliadin (the principal protein from the
quantity viewpoint in wheat), carbohydrates, fats, and mineral salts. In
spite of the fact that the nitrogen of this mixture was sufficient to
supply the body needs, as proved by analysis of the excreta, the animals
steadily declined in weight from the time they were confined to this diet.
The authors had assumed that the gliadin was deficient in a substance
necessary to growth (lysine) but since their studies were begun only after