These researches were published as a bulletin (No. 156) by the Carnegie
Institution in 1911, the same year that Funk announced his Vitamine
discoveries. It was timely in this respect for one of Osborne and Mendel's
discoveries was that no matter how efficient the mixture in all the
requirements then known to the nutrition expert, the rats failed to grow
unless there was added to the diet a factor which they found in milk. In
searching for this factor they made a still further discovery for on
fractioning the milk they soon learned that the unknown factor was
distributed in two different parts of the milk, namely in the butter fat
and in the protein free and fat-free whey. The absence of either milk
fraction was sufficient to prevent growth. The 1911 publication merely
described these results without attempting to explain the nature of the
growth producing factors but the vitamine hypothesis of Funk naturally
suggested to these authors that their two unknown factors might be similar
in nature to his beri-beri curative factor and their announcement may be
justly considered a point of junction of nutrition theories with the
vitamine hypothesis.

The peculiarity of butter fat as a growth stimulus had been considered
from another angle by a German worker, Stepp. In 1909 this student of
nutrition had tried to estimate the importance of various types of fats in
the same way that was later done with proteins, to determine whether, like
proteins, the quality of the fats varied in nutritive efficiency. His
experiments were also conducted with white rats and the main outlines of
his methods and observations were as follows: Rats fed on a bread and milk
diet grew normally. If now the bread and milk mixture was extracted with
alcohol-ether the residue was found to be inadequate for growth or
maintenance. Stepp assumed that this failure could naturally be ascribed
to the removal of the fat by the alcohol-ether mixture. To determine the
efficiency of different kinds of fats he then proceeded to substitute in