ters obstacles at every step. For me, on the contrary,
these transformations present a common character,
namely, that of taking place, every one of them, in
the presence of an organic substance in the process of
decomposition. We start a lactic or butyric fermen-
tation by means of old cheese, or putrid meat. As for
the alcoholic fermentation, Colin showed in 1828, that
this could be provoked by means of many organic
nitrogenous substances, different from the yeast of
beer, provided that they are in process of decomposition.
It is these dead substances which form the ferment.
I do not forget the experiments of Thénard on the almost
constant production of yeast in juices when in fermen-
tation; I do not forget, furthermore, the conclusions
of Cagniard-Latour and Schwann confirmed by Quevenne,
Turpin, and Mitscherlich. But this yeast does not
embarrass me, it enters into my system. If you admit
that it lives, then you admit also that it dies. Now,
it is in dying that it acts, as a result of the decomposition
which it undergoes at this moment and of that Thénard
furnishes us the proof."

That savant had seen, in fact, that by adding 20 parts
of yeast to 100 parts of cane-sugar in solution in water,
he obtained a rapid and regular fermentation, after
which the remaining yeast collected on a filter weighed
no more than 13.3 grams. Added to a fresh and equal
quantity of sugar, this residue produced a fermentation
more slowly than the first time, after which it was
reduced to 10 grams, and was incapable of producing
a new fermentation. What more fitting to demon-
strate that the yeast destroys itself and is consumed by
its own activity? The theory of Liebig finds a good
defense, therefore, from this point of view. As for the
undeniable multiplication of the yeast in the vat of the
brewery, in the manufacture of wine, especially of the

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