a question which, with just reciprocity, these same studies
permitted him to solve. Whence come the ferments?
Are they organized spontaneously at the expense of
dead organic matter? Or, do they come in the regular
ways from organisms like themselves, and from pre-
existing germs? Here we have a question which had
been asked very often, ever since men had begun to reflect,
and which had been solved in very different ways.
Pasteur, himself, at the close of his studies on crystallog-
raphy, had been very undecided, and I think also very
indifferent regarding the answer. He had no precon-
ceived ideas: he would accept the results of experi-
mentation. But at the point to which the study of
fermentations had led him, he could no longer believe
in spontaneous generation: it is too far removed from
the idea of specificity, which he had just introduced
into science. Everywhere around us the idea of
species accompanies the idea of continuance by the
germ cell, and it would be very astonishing if this order
were changed in the world of the infinitely little.

The ancients believed in the spontaneous generation of
eels from the ooze of rivers, and in that of bees in the
entrails of a dead bull. But these were the ideas of a
child who had never lived in the face of the progress of
knowledge. For a long time people had believed in the
spontaneous generation of worms in putrefying meat,
because in this case the experiment is more difficult or
the observation is more delicate, and a Redi was neces-
sary to demonstrate that these worms come from eggs
laid by flies, and that one would no longer see them in a
piece of meat which was protected by a simple layer of
gauze. It is true that this piece of meat continued to
putrefy, to decay, and to nourish, no longer worms but
confused tribes of microscopic organisms. As long as
it was the belief that fermentation and putrefaction oc-

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