tely 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 out of the bottom story, the result of which is that all the
others fall.

As chemistry advanced, facts came to light which put a new face upon
Stahl's hypothesis, and gave it a safer foundation than it previously
possessed. The general nature of these phenomena may be