white wines, Liebig, who had much imagination, had
an explanation all ready. All the fermentable liquids
contain what he called gluten, what we would call to-day
albuminoid substances. In contact with air this
gluten oxidized and was precipitated in the form of
yeast: this is the explanation of the experiment of Gay-
Lussac. Consequently, in proportion as one part of
the yeast destroys itself by acting on the fermentable
substance, another forms: if more is formed than is
destroyed we have the case of the brewery vats; if
more is destroyed than is formed, we have the case of
Thénard's experiments concerning which we have just
spoken.

For the fundamental explanation of the phenomena,
Liebig had only to take the ideas of Willis and of Stahl
on the internal movement of a mass in fermentation,
attributing the motive power to the ferment. "The
yeast of beer, and in general all animal and plant sub-
stances undergoing putrefaction, impart to other sub-
stances the state of decomposition in which they find
themselves. The movement which is imparted to
their own elements, as the result of the disturbance of
the equilibrium, is communicated equally to the elements
of the substances which are found in contact with them."
For example, sugar is a stable compound with respect
to a great number of external influences, air, light, even
heat. On the contrary, it is an unstable structure with
respect to the molecular movement of organic sub-
stances in decomposition: under their action it breaks
up easily into alcohol and carbonic acid.

Thus the theory of Liebig, without denying or accept-
ing formally the organization of the yeast globule,
confined itself to denying its vital rôle in fermentation,
and collected all these phenomena into one single
formula. From all sides, it presented a good face,

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