Yeast | Page 7

of our own muscles, which forms
the chief part of our own blood, which forms the chief part of the white
of the egg; that, in fact, although this little organism is a plant, and
nothing but a plant, yet that its active living contents contain a
substance which is called "protein," which is of the same nature as the
substance which forms the foundation of every animal organism
whatever.
Now we come next to the question of the analysis of the products, of
that which is produced during the process of fermentation. So far back
as the beginning of the 16th century, in the times of transition between
the old alchemy and the modern chemistry, there was a remarkable man,
Von Helmont, a Dutchman, who saw the difference between the air
which comes out of a vat where something is fermenting and common
air. He was the man who invented the term "gas," and he called this
kind of gas "gas silvestre"--so to speak gas that is wild, and lives in out
of the way places--having in his mind the identity of this particular kind
of air with that which is found in some caves and cellars. Then, the
gradual process of investigation going on, it was discovered that this
substance, then called "fixed air," was a poisonous gas, and it was
finally identified with that kind of gas which is obtained by burning
charcoal in the air, which is called "carbonic acid." Then the substance
alcohol was subjected to examination, and it was found to be a
combination of carbon, and hydrogen, and oxygen. Then the sugar
which was contained in the fermenting liquid was examined and that
was found to contain the three elements carbon, hydrogen, and oxygen.
So that it was clear there were in sugar the fundamental elements which
are contained in the carbonic acid, and in the alcohol. And then came
that great chemist Lavoisier, and he examined into the subject carefully,
and possessed with that brilliant thought of his which happens to be
propounded exactly apropos to this matter of fermentation--that no
matter is ever lost, but that matter only changes its form and changes its
combinations--he endeavoured to make out what became of the sugar
which was subjected to fermentation. He thought he discovered that the
whole weight of the sugar was represented by the carbonic acid
produced; that in other words, supposing this tumbler to represent the
sugar, that the action of fermentation was as it were the splitting of it,

the one half going away in the shape of carbonic acid, and the other
half going away in the shape of alcohol. Subsequent inquiry, careful
research with the refinements of modern chemistry, have been applied
to this problem, and they have shown that Lavoisier was not quite
correct; that what he says is quite true for about 95 per cent. of the
sugar, but that the other 5 per cent., or nearly so, is converted into two
other things; one of them, matter which is called succinic acid, and the
other matter which is called glycerine, which you all know now as one
of the commonest of household matters. It may be that we have not got
to the end of this refined analysis yet, but at any rate, I suppose I may
say--and I speak with some little hesitation for fear my friend Professor
Roscoe here may pick me up for trespassing upon his province--but I
believe I may say that now we can account for 99 per cent. at least of
the sugar, and that 99 per cent. is split up into these four things,
carbonic acid, alcohol, succinic acid, and glycerine. So that it may be
that none of the sugar whatever disappears, and that only its parts, so to
speak, are re-arranged, and if any of it disappears, certainly it is a very
small portion.
Now these are the facts of the case. There is the fact of the growth of
the yeast plant; and there is the fact of the splitting up of the sugar.
What relation have these two facts to one another?
For a very long time that was a great matter of dispute. The early
French observers, to do them justice, discerned the real state of the case,
namely, that there was a very close connection between the actual life
of the yeast plant and this operation of the splitting up of the sugar; and
that one was in some way or other connected with the other. All
investigation subsequently has confirmed this original idea. It has been
shown that if you take any measures by which other plants of like kind
to the torula would be killed, and by which the yeast plant is killed,
then the yeast loses its efficiency. But