actually obtained some microscopic fibrous needles which were curative.
These needles however on recrystallization resulted in the production of
a compound contaminated with adenin or rather in adenin contaminated with
the curative substance and on standing for some time the adenin crystals
gradually lost their curative power. These results led Williams to suggest
an interesting hypothesis. By experiments conducted with the hydroxy-
pyridines he believed that he had demonstrated a relation between
tautomerism or changed space relations in these sort of substances and
curative properties. He states his view as follows:

The vitamines contain one or more groups of atoms constituting nuclei in
which the curative properties are resident. In a free state these nuclei
possess the vitamine activity but under ordinary conditions are
spontaneously transformed into isomers which do not possess an
antineuritic power. The complementary substances or substituent groups
with which these nuclei are more or less firmly combined in nature exert a
stabilizing and perhaps otherwise favorable influence on the curative
nucleus, but do not themselves possess the vitamine type of physiological
potency. Accordingly it is believed that while partial cleavage of the
vitamines may result only in a modification of their physiological
properties, by certain means disruption may go so far as to effect a
complete separation of nucleus and stabilizer, and if it does so will be
followed by a loss of curative power due to isomerism. The basis for the
assumption that an isomerization constitutes the final and physiologically
most significant step in the inactivation of a vitamine is found in the
studies of synthetic antineuritic products. This assumption is supported
by evidence ... of the existence of such isomerism in the crystalline
antineuritic substances obtainable from brewer's yeast.

According to this view the active adenin obtained was not a contamination