pictures of banquets in which the wine-cup passes round, graven on the
walls of their tombs. A knowledge of the process of fermentation,
therefore, was in all probability possessed by the prehistoric
populations of the globe; and it must have become a matter of great
interest even to primaeval wine-bibbers to study the methods by which
fermented liquids could be surely manufactured. No doubt it was soon
discovered that the most certain, as well as the most expeditious, way of
making a sweet juice ferment was to add to it a little of the scum, or
lees, of another fermenting juice. And it can hardly be questioned that
this singular excitation of fermentation in one fluid, by a sort of
infection, or inoculation, of a little ferment taken from some other
fluid, together with the strange swelling, foaming, and hissing of the
fermented substance, must have always attracted attention from the more
thoughtful. Nevertheless, the commencement of the scientific analysis of
the phenomena dates from a period not earlier than the first half of the
seventeenth century.

At this time, Van Helmont made a first step, by pointing out that the
peculiar hissing and bubbling of a fermented liquid is due, not to the
evolution of common air (which he, as the inventor of the term "gas,"
calls "gas ventosum"), but to that of a peculiar kind of air such as is
occasionally met with in caves, mines, and wells, and which he calls "gas
sylvestre."

But a century elapsed before the nature of this "gas sylvestre," or, as
it was afterwards called, "fixed air," was clearly determined, and it was
found to be identical with that deadly "choke-damp" by which the lives of
those who descend into old wells, or mines, or brewers' vats, are
sometimes suddenly ended; and with the poisonous aëriform fluid which is
produced by the combustion of charcoal, and now goes by the name of