iver's Travels_. As a specimen of the writer's humour, his account
of what happens when fermentation comes to an end may suffice. "Sobald
naemlich die Thiere keinen Zucker mehr vorfinden, so fressen sie sich
gegenseitig selbst auf, was durch eine eigene Manipulation geschieht;
alles wird verdant bis auf die Eier, welche unveraendert durch den
Darmkanal hineingehen; man hat zuletzt wieder gaehrungsfaehige Hefe,
naemlich den Saamen der Thiere, der uebrig bleibt."] However, it may be
asked, is there any necessary opposition between the so-called "vital"
and the strictly physico-chemical views of fermentation? It is quite
possible that the living _Torula_ may excite fermentation in sugar,
because it constantly produces, as an essential part of its vital
manifestations, some substance which acts upon the sugar, just as the
synaptase acts upon the amygdalin. Or it may be, that, without the
formation of any such special substance, the physical condition of the
living tissue of the yeast plant is sufficient to effect that small
disturbance of the equilibrium of the particles of the sugar, which
Lavoisier thought sufficient to effect its decomposition.

Platinum in a very fine state of division--known as platinum black, or
_noir de platine_--has the very singular property of causing alcohol to
change into acetic acid with great rapidity. The vinegar plant, which is
closely allied to the yeast plant, has a similar effect upon dilute
alcohol, causing it to absorb the oxygen of the air, and become converted
into vinegar; and Liebig's eminent opponent, Pasteur, who has done so
much for the theory and the practice of vinegar-making, himself suggests
that in this case--

"La cause du phenomene physique qui accompagne la vie de la plante reside
dans un etat physique propre, analogue a celui du noir de platine. Mais
il est essentiel de remarquer que cet etat physique de la plante est
etroitement lie avec la vie de cette plante."[5]

[Footnote 5: _Etudes sur les Mycodermes_, Comptes-Rendus, liv., 1862.]

Now, if the vinegar plant gives rise to the oxidation of alcohol, on
account of its merely physical constitution, it is at any rate possible
that the physical constitution of the yeast plant may exert a decomposing
influence on sugar.

But, without presuming to discuss a question which leads us into the very
arcana of chemistry, the present state of speculation upon the _modus
operandi_ of the yeast plant in producing fermentation is