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not less remarkable than that of the microscopist。 The chemist
discovered that the yeast plant being composed of a sort of bag； like a
bladder； inside which is a peculiar soft； semifluid materialthe
chemist found that this outer bladder has the same composition as the
substance of wood； that material which is called 〃cellulose；〃 and which
consists of the elements carbon and hydrogen and oxygen； without any
nitrogen。 But then he also found （the first person to discover it was
an Italian chemist； named
Fabroni； in the end of the last century） that this inner matter which
was contained in the bag； which constitutes the yeast plant； was a
substance containing the elements carbon and hydrogen and oxygen and
nitrogen； that it was what Fabroni called a vegeto…animal substance；
and that it had the peculiarities of what are commonly called 〃animal
products。〃
This again was an exceedingly remarkable discovery。 It lay neglected
for a time； until it was subsequently taken up by the great chemists of
modern times； and they； with their delicate methods of analysis； have
finally decided that； in all essential respects； the substance which
forms the chief part of the contents of the yeast plant is identical
with the material which forms the chief part 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 placeshaving 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
fermentationthat no matter is ever lost； but that matter only changes
its form and changes its combinationshe 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 sayand I speak with some little hesitation
for fear my friend Professor Roscoe here may pick me up for trespassing
upon his provincebut 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 a capital
experiment upon this subject was made by a very distinguished man；
Helmholz； who performed an experiment of this kind。 He had two
vesselsone of them we will suppose full of yeast； but over the bottom
of it； as this might be； was tied a thin film of bladder； consequently；
through that thin film of bladder all the liquid parts of the yeast
would go； but the solid parts would be stopped behind； the torula would
be stopped； the liquid parts of the yeast would go。 And then he took
another vessel containing a fermentable solution of sugar； and he put
one inside the other； and in this way you see the fluid parts of the
yeast were able to pass through with the utmost ease into the sugar； but
the solid parts could not get through at all。 And he judged thus： if
the fluid parts are those which excite fermentation； then； inasmuch as
these are stopped； the sugar will not ferment； and the sugar did not
ferment； showing quite clearly； that an immediate contact with the
solid； living torula was absolutely necessary to excite this process of
splitting up of the sugar。 This experiment was quite conclusive as to
this particular point； and has had very great fruits in other
directions。
Well； then； the yeast plant being essential to the production of
fermentation； where does the yeast plant come from？ Here； again； was
another great problem opened up； for； as I said at starting； you have；
under ordinary circumstances in warm weathe