The experiments, when repeated, were not always
successful, especially when, instead of working with
sugared musts, organic infusions were used. But how
separate, in their causes and origins, phenomena so
evidently analogous as fermentation and putrefaction?
Opinion remained, therefore, a little hesitating, and the
best proof that the old ideas were not disturbed is the
work of Helmholtz published in 1843, the first work of
the illustrious physicist.

Helmholtz repeated with success the experiment
of Schwann, and asked himself what is this something
in the air which heat kills, or renders inactive.
It may be, he said, only a putrid exhalation coming
from a mass undergoing fermentation, and capable,
by virtue of an unknown power, of provoking a new
fermentation: or else it is a living germ. In the latter
case, the germ is insoluble in water. The putrid ex-
halation is, on the contrary, soluble and therefore dif-
fusible. Let us take, therefore, two vessels separated
by a membrane; in one let us place a liquid under-
going fermentation, or putrefying, in the other a liquid
of the same nature but not fermenting, and let us see
what will happen. If the fermentation does not
cross the membrane, then it is produced by living
creatures; if it does pass the membrane, it must be
attributed to something else.

Now the experiment is always successful with liquids
undergoing alcoholic fermentation, and rarely or never
with macerated meat. That is, the presence of the
membrane prevents the alcoholic fermentation from
passing, but does not arrest the cause of putrefaction,
whatever it may be. From this Helmholtz concludes
that there are two kinds of transformation of organic
matter, one which takes place with the concourse of
microscopic organisms, and the other without them.

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