carbonic acid gas, which are the two great and conspicuous products of
fermentation. And finally, in 1787, the Italian chemist, Fabroni, made
the capital discovery that the yeast ferment, the presence of which
is necessary to fermentation, is what he termed a "vegeto-animal"
substance--or is a body which gives off ammoniacal salts when it is
burned, and is, in other ways, similar to the gluten of plants and the
albumen and casein of animals.

These discoveries prepared the way for the illustrious Frenchman,
Lavoisier, who first approached the problem of fermentation with a
complete conception of the nature of the work to be done. The words
in which he expresses this conception, in the treatise on elementary
chemistry to which reference has already been made, mark the year 1789
as the commencement of a revolution of not less moment in the world of
science than that which simultaneously burst over the political world,
and soon engulfed Lavoisier himself in one of its mad eddies.

"We may lay it down as an incontestable axiom that, in all the
operations of art and nature, nothing is created; an equal quantity
of matter exists both before and after the experiment: the quality and
quantity of the elements remain precisely the same, and nothing takes
place beyond changes and modifications in the combinations of these
elements. Upon this principle, the whole art of performing chemical
experiments depends; we must always suppose an exact equality between
the elements of the body examined and those of the products of its
analysis.

"Hence, since from must of grapes we procure alcohol and carbonic
acid, I have an undoubted right to suppose that must consists of
carbonic acid and alcohol. From these premisses we have two modes