of the attempt to understand the relation between the yeast and the
products； and lastly； what very curious side issues if I may so call
themhave branched out in the course of this inquiry； which has now
occupied somewhere about two centuries。
The first thing was to make out precisely and clearly what was the
nature of this substance； this apparently mere scum and mud that we
call yeast。 And that was first commenced seriously by a wonderful old
Dutchman of the name of Leeuwenhoek； who lived some two hundred years
ago； and who was the first person to invent thoroughly trustworthy
microscopes of high powers。 Now； Leeuwenhoek went to work upon this
yeast mud； and by applying to it high powers of the microscope； he
discovered that it was no mere mud such as you might at first suppose；
but that it was a substance made up of an enormous multitude of minute
grains； each of which had just as definite a form as if it were a grain
of corn； although it was vastly smaller； the largest of these not being
more than the two…thousandth of an inch in diameter； while； as you
know； a grain of corn is a large thing； and the very smallest of these
particles were not more than the seven…thousandth of an inch in
diameter。 Leeuwenhoek saw that this muddy stuff was in reality a
liquid； in which there were floating this immense number of definitely
shaped particles； all aggregated in heaps and lumps and some of them
separate。 That discovery remained； so to speak； dormant for fully a
century； and then the question was taken up by a French discoverer；
who； paying great attention and having the advantage of better
instruments than Leeuwenhoek had； watched these things and made the
astounding discovery that they were bodies which were constantly being
reproduced and growing； than when one of these rounded bodies was once
formed and had grown to its full size； it immediately began to give off
a little bud from one side； and then that bud grew out until it had
attained the full size of the first； and that； in this way； the yeast
particle was undergoing a process of multiplication by budding； just as
effectual and just as complete as the process of multiplication of a
plant by budding； and thus this Frenchman； Cagniard de la Tour； arrived
at the conclusionvery creditable to his sagacity； and which has been
confirmed by every observation and reasoning sincethat this
apparently muddy refuse was neither more nor less than a mass of
plants； of minute living plants； growing and multiplying in the sugary
fluid in which the yeast is formed。 And from that time forth we have
known this substance which forms the scum and the lees as the yeast
plant； and it has received a scientific namewhich I may use without
thinking of it； and which I will therefore give younamely； 〃Torula。〃
Well； this was a capital discovery。 The next thing to do was to make
out how this torula was related to the other plants。 I won't weary you
with the whole course of investigation； but I may sum up its results；
and they are thesethat the torula is a particular kind of a fungus； a
particular state rather； of a fungus or mould。 There are many moulds
which under certain conditions give rise to this torula condition； to a
substance which is not distinguishable from yeast； and which has the
same properties as yeastthat is to say； which is able to decompose
sugar in the curious way that we shall consider by…and…by。 So that the
yeast plant is a plant belonging to a group of the Fungi； multiplying
and growing and living in this very remarkable manner in the sugary
fluid which is； so to speak； the nidus or home of the yeast。
That； in a few words； is； as far as investigationby the help of one's
eye and by the help of the microscopehas taken us。 But now there is
an observer whose methods of observation are more refined than those of
men who use their eye； even though it be aided by the microscope； a man
who sees indirectly further than we can see directlythat is； the
chemist； and the chemist took up this question； and his discovery was
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； th