substance. This adsorbent has been found quite as effective as the
fuller's earth and it is possible to recover the vitamine from the carbon
with treatment by acid. Glacial acetic and heat are especially favorable
for this process. The study of this concentrate has not, however, yet
reached a stage where it contributes any real data on the subject but
merely provides another method for forming concentrates.

If we were to characterize the present status of the search for the "B"
type it might be said to have resolved itself into obtaining concentrates
of high potency as the first step in the process and this type of
investigation is now going on in many laboratories.

If the data is then meagre in the field of the "B" vitamine it is still
more limited in the case of the "A" and the "C." One of the earliest
difficulties encountered in the study of the "A" vitamine was the failure
of fat solvents to extract the material from its richest vegetable
sources. If butter or egg yolk is extracted with ether, the fat obtained
is rich in the "A" vitamine. If, however, ether-extraction is applied to
green leaves or seeds it removes the oils but these oils contain little or
no vitamine. Pressing methods also fail to remove the substance from
vegetable sources. For example, if we press or extract cotton seed we
obtain the oil but the vitamine is retained in the press cake. McCollum
suggested the following explanation for this behavior. His idea is that
the "A" vitamine while soluble in fat is so bound up in the vegetable
source that extraction methods fail to loosen it. When these vegetables
are eaten the vitamine is set free in the process of digestion and being
fat-soluble passes into solution in the animal fats. Hence, when these
fats contain it in solution, they retain it in the process of extraction
while, lacking this separatory process, ether fails to loosen it from the
vegetable binding. Recently, however, Osborne and Mendel have presented