Thus Lavoisier thought he had demonstrated that the carbonic acid and
the alcohol which are produced by the process of fermentation, are
equal in weight to the sugar which disappears; but the application of
the more refined methods of modern chemistry to the investigation of
the products of fermentation by Pasteur, in 1860, proved that this is
not exactly true, and that there is a deficit of from 5 to 7 per cent.
of the sugar which is not covered by the alcohol and carbonic acid
evolved. The greater part of this deficit is accounted for by the
discovery of two substances, glycerine and succinic acid, of the
existence of which Lavoisier was unaware, in the fermented liquid.
But about 1-1/2 per cent. still remains to be made good. According to
Pasteur, it has been appropriated by the yeast, but the fact that such
appropriation takes place cannot be said to be actually proved.

However this may be, there can be no doubt that the constituent
elements of fully 98 per cent. of the sugar which has vanished during
fermentation have simply undergone rearrangement; like the soldiers
of a brigade, who at the word of command divide themselves into the
independent regiments to which they belong. The brigade is sugar, the
regiments are carbonic acid, succinic acid, alcohol, and glycerine.

From the time of Fabroni, onwards, it has been admitted that the agent
by which this surprising rearrangement of the particles of the sugar
is effected is the yeast. But the first thoroughly conclusive evidence
of the necessity of yeast for the fermentation of sugar was furnished
by Appert, whose method of preserving perishable articles of food
excited so much attention in France at the beginning of this century.
Gay-Lussac, in his "Mémoire sur la Fermentation,"[1] alludes to
Appert's method of preserving beer-wort unfermented for an indefinite