; and he found that if he boiled any of these substances
and then tied them so as to exclude the air, that they would be
preserved for any time. He tried these experiments, particularly with
the must of wine and with the wort of beer; and he found that if the
wort of beer had been carefully boiled and was stopped in such a way
that the air could not get at it, it would never ferment. What was the
reason of this? That, again, became the subject of a long string of
experiments, with this ultimate result, that if you take precautions to
prevent any solid matters from getting into the must of wine or the wort
of beer, under these circumstances--that is to say, if the fluid has
been boiled and placed in a bottle, and if you stuff the neck of the
bottle full of cotton wool, which allows the air to go through and stops
anything of a solid character however fine, then you may let it be for
ten years and it will not ferment. But if you take that plug out and
give the air free access, then, sooner or later fermentation will set
up. And there is no doubt whatever that fermentation is excited only by
the presence of some torula or other, and that that torula proceeds in
our present experience, from pre-existing torulae. These little bodies
are excessively light. You can easily imagine what must be the weight of
little particles, but slightly heavier than water, and not more than the
two-thousandth or perhaps seven-thousandth of an inch in diameter. They
are capable of floating about and dancing like motes in the sunbeam;
they are carried about by all sorts of currents of air; the great
majority of them perish; but one or two, which may chance to enter into
a sugary solution, immediately enter into active life, find there the
conditions of their nourishment, increase and multiply, and may give
rise to any quantity whatever of this substance yeast. And, whatever
may be true or not be true about this "spontaneous generation," as it
is called in regard to all other kinds of living things, it is perfectly
certain, as regards yeast, that it always owes its origin to this
process of transportation or inoculation, if you like so to call it,
from some other living yeast organism; and so far as yeast is concerned,
the doctrine of spontaneous generation is absolutely out of court.
And not only so, but the yeast must be alive in order to exert these
peculiar properties. If it be crushed, if it be heated so far that its
life is destroyed, that pe