Yeast | Page 9

yeast must be alive in order to exert these peculiar properties. If it
be crushed, if it be heated so far that its life is destroyed, that peculiar
power of fermentation is not excited. Thus we have come to this
conclusion, as the result of our inquiry, that the fermentation of sugar,
the splitting of the sugar into alcohol and carbonic acid, glycerine, and
succinic acid, is the result of nothing but the vital activity of this little
fungus, the torula.
And now comes the further exceedingly difficult inquiry--how is it that
this plant, the torula, produces this singular operation of the splitting up
of the sugar? Fabroni, to whom I referred some time ago, imagined that
the effervescence of fermentation was produced in just the same way as
the effervescence of a sedlitz powder, that the yeast was a kind of acid,
and that the sugar was a combination of carbonic acid and some base to
form the alcohol, and that the yeast combined with this substance, and
set free the carbonic acid; just as when you add carbonate of soda to
acid you turn out the carbonic acid. But of course the discovery of
Lavoisier that the carbonic acid and the alcohol taken together are very

nearly equal in weight to the sugar, completely upset this hypothesis.
Another view was therefore taken by the French chemist, Thenard, and
it is still held by a very eminent chemist, M. Pasteur, and their view is
this, that the yeast, so to speak, eats a little of the sugar, turns a little of
it to its own purposes, and by so doing gives such a shape to the sugar
that the rest of it breaks up into carbonic acid and alcohol.
Well, then, there is a third hypothesis, which is maintained by another
very distinguished chemist, Liebig, which denies either of the other two,
and which declares that the particles of the sugar are, as it were, shaken
asunder by the forces at work in the yeast plant. Now I am not going to
take you into these refinements of chemical theory, I cannot for a
moment pretend to do so, but I may put the case before you by an
analogy. Suppose you compare the sugar to a card house, and suppose
you compare the yeast to a child coming near the card house, then
Fabroni's hypothesis was that the child took half the cards away;
Thenard's and Pasteur's hypothesis is that the child pulls out the bottom
card and thus makes it tumble to pieces; and Liebig's hypothesis is that
the child comes by and shakes the table and tumbles the house down. I
appeal to my friend here (Professor Roscoe) whether that is not a fair
statement of the case.
Having thus, as far as I can, discussed the general state of the question,
it remains only that I should speak of some of those collateral results
which have come in a very remarkable way out of the investigation of
yeast. I told you that it was very early observed that the yeast plant
consisted of a bag made up of the same material as that which
composes wood, and of an interior semifluid mass which contains a
substance, identical in its composition, in a broad sense, with that
which constitutes the flesh of animals. Subsequently, after the structure
of the yeast plant had been carefully observed, it was discovered that all
plants, high and low, are made up of separate bags or "cells," as they
are called; these bags or cells having the composition of the pure matter
of wood; having the same composition, broadly speaking, as the sac of
the yeast plant, and having in their interior a more or less fluid
substance containing a matter of the same nature as the protein
substance of the yeast plant. And therefore this remarkable result came
out--that however much a plant may differ from an animal, yet that the
essential constituent of the contents of these various cells or sacs of

which the plant is made up, the nitrogenous protein matter, is the same
in the animal as in the plant. And not only was this gradually
discovered, but it was found that these semifluid contents of the plant
cell had, in many cases, a remarkable power of contractility quite like
that of the substance of animals. And about 24 or 25 years ago, namely,
about the year 1846, to the best of my recollection, a very eminent
German botanist, Hugo Von Mohl, conferred upon this substance
which is found in the interior of the plant cell, and which is identical
with the matter found in the inside of the yeast cell, and which again
contains an animal substance similar to that of which we ourselves are
made up--he conferred