fact of the splitting up of the sugar.
What relation have these two facts to one another?

For a very long time that was a great matter of dispute. The early
French observers, to do them justice, discerned the real state of the
case, namely, that there was a very close connection between the actual
life of the yeast plant and this operation of the splitting up of the
sugar; and that one was in some way or other connected with the other.
All investigation subsequently has confirmed this original idea. It has
been shown that if you take any measures by which other plants of like
kind to the torula would be killed, and by which the yeast plant is
killed, then the yeast loses its efficiency. But 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
seem