evisioe_, from a _Mucor_, a mould allied
to _Penicillium_.

It follows, therefore, that the _Toruloe_, or organisms of yeast, are
veritable plants; and conclusive experiments have proved that the power
which causes the rearrangement of the molecules of the sugar is
intimately connected with the life and growth of the plant. In fact,
whatever arrests the vital activity of the plant also prevents it from
exciting fermentation.

Such being the facts with regard to the nature of yeast, and the changes
which it effects in sugar, how are they to be accounted for? Before
modern chemistry had come into existence, Stahl, stumbling, with the
stride of genius, upon the conception which lies at the bottom of all
modern views of the process, put forward the notion that the ferment,
being in a state of internal motion, communicated that motion to the
sugar, and thus caused its resolution into new substances. And Lavoisier,
as we have seen, adopts substantially the same view. But Fabroni, full of
the then novel conception of acids and bases and double decompositions,
propounded the hypothesis that sugar is an oxide with two bases, and the
ferment a carbonate with two bases; that the carbon of the ferment unites
with the oxygen of the sugar, and gives rise to carbonic acid; while the
sugar, uniting with the nitrogen of the ferment, produces a new substance
analogous to opium. This is decomposed by distillation, and gives rise to
alcohol. Next, in 1803, Thenard propounded a hypothesis which partakes
somewhat of the nature of both Stahl's and Fabroni's views. "I do not
believe with Lavoisier," he says, "that all the carbonic acid formed
proceeds from the sugar. How, in that case, could we conceive the action
of the ferment on it? I think that the first portions of the acid are due
to a combination of the carbon of the ferment with the oxygen of the
sugar, and that it is by carrying off a portion of oxygen from the last
that the ferment causes the fermentation to commence--the equilibrium
between the principles of the sugar being disturbed, they combine afresh
to form carbonic acid and alcohol."

The three views here before us may be familiarly exemplified by supposing
the sugar to be a card-house. According to Stahl, the ferment is somebody
who knocks the table, and shakes the card-house down; according to
Fabroni, the ferment takes out some cards, but puts others in their
places; according to Thenard, the ferment simply takes a card o