Yeast | Page 8

a capital experiment upon this
subject was made by a very distinguished man, Helmholz, who
performed an experiment of this kind. He had two vessels--one of them
we will suppose full of yeast, but over the bottom of it, as this might be,
was tied a thin film of bladder; consequently, through that thin film of
bladder all the liquid parts of the yeast would go, but the solid parts
would be stopped behind; the torula would be stopped, the liquid parts
of the yeast would go. And then he took another vessel containing a

fermentable solution of sugar, and he put one inside the other; and in
this way you see the fluid parts of the yeast were able to pass through
with the utmost ease into the sugar, but the solid parts could not get
through at all. And he judged thus: if the fluid parts are those which
excite fermentation, then, inasmuch as these are stopped, the sugar will
not ferment; and the sugar did not ferment, showing quite clearly, that
an immediate contact with the solid, living torula was absolutely
necessary to excite this process of splitting up of the sugar. This
experiment was quite conclusive as to this particular point, and has had
very great fruits in other directions.
Well, then, the yeast plant being essential to the production of
fermentation, where does the yeast plant come from? Here, again, was
another great problem opened up, for, as I said at starting, you have,
under ordinary circumstances in warm weather, merely to expose some
fluid containing a solution of sugar, or any form of syrup or vegetable
juice to the air, in order, after a comparatively short time, to see all
these phenomena of fermentation. Of course the first obvious
suggestion is, that the torula has been generated within the fluid. In fact,
it seems at first quite absurd to entertain any other conviction; but that
belief would most assuredly be an erroneous one.
Towards the beginning of this century, in the vigorous times of the old
French wars, there was a Monsieur Appert, who had his attention
directed to the preservation of things that ordinarily perish, such as
meats and vegetables, and in fact he laid the foundation of our modern
method of preserving meats; 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