s 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 peculiar power of fermentation is not excited.
Thus we have come to this conclusion, as the result of our inquiry, that
the fermentation of sugar, the splitting of the sugar into alcohol and
carbonic acid, glycerine, and succinic acid, is the result of nothing
but the vital activity of this little fungus, the torula.

And now comes the further exceedingly difficult inquiry--how is it
that this plant, the torula, produces this singular operation of the
splitting up of the sugar? Fabroni, to whom I referred some time ago,
imagined that the effervescence of fermentation was produced in just the
same way as the effervescence of a sedlitz powder, that the yeast was a
kind of acid, and that the sugar was a combination of carbonic acid and
some base to form the alcohol, and that the yeast combined with
this substance, and set free the carbonic acid; just as when you add
carbonate of soda to acid you turn out the carbonic acid. But of course
the discovery of Lavoisier that the carbonic acid and the alcohol taken
together are very nearly equal in weight to the sugar, completely upset
this hypothesis. Another view was therefore taken by the French chemist,
Thenard, and it is still held by a very eminent chemist, M. Pasteur, and
their view is this, that the yeast, so to speak, eats a little of the
sugar, turns a little of it to its own purposes, and by so doing gives
such a shape to the sugar that the rest of it breaks up into carbonic
acid and alcohol.

Well, then, there is a third hypothesis, which is maintained by another
very distinguished chemist, Liebig, which denies either of the other
two, and which declares that the particles of the sugar are, as it were,
shaken asunder by the forces at work in the yeast plant. Now I am not
going to take you into these refinements of chemical theory, I cannot
for a moment pretend to do so, but I may put the case before you by an
analogy. Suppose you compare the sugar to a card house, and suppose you
compare the yeast to a child coming near the card house, then Fabroni's
hypo