,,yeast  ,by ,thomas ,h4 ,huxley    ,i  
,,have selected to-night the particular 
subject of ,yeast for two reasons--or1  
rather1 ,i should say for three4 ,in the
 first place1 because it is one of the  
simplest and the most familiar objects  
with which we are acquainted4 ,in the   
second place1 because the facts and     
phenomena which ,i have to describe are 
so simple that it is possible to put    
them before you without the help of any 
of those pictures or diagrams which are 
needed when matters are more            
complicated1 and which1 if ,i had to    
refer to them here1 would involve the   
necessity of my turning away from you   
now and then1 and thereby increasing    
very largely my difficulty 7already     
sufficiently great7 in making myself    
heard4 ,and thirdly1 ,i have chosen this
 subject because ,i know of no familiar 
substance forming part of our every-day 
knowledge and experience1 the           
examination of which1 with a little     
care1 tends to open up such very        

considerable issues as does this        
substance--yeast4  ,in the first place1 
,i should like to call your attention to
 a fact with which the whole of you are1
 to begin with1 perfectly acquainted1 ,i
 mean the fact that any liquid          
containing sugar1 any liquid which is   
formed by pressing out the succulent    
parts of the fruits of plants1 or a     
mixture of honey and water1 if left to  
itself for a short time1 begins to      
undergo a peculiar change4 ,no matter   
how clear it might be at starting1 yet  
after a few hours1 or at most a few     
days1 if the temperature is high1 this  
liquid begins to be turbid1 and         
by-and-by bubbles make their appearance 
in it1 and a sort of dirty-looking      
yellowish foam or scum collects at the  
surface2 while at the same time1 by     
degrees1 a similar kind of matter1 which
 we call the lees1 sinks to the bottom4 
,the quantity of this dirty-looking     
stuff1 that we call the scum and the    
lees1 goes on increasing until it       

reaches a certain amount1 and then it   
stops2 and by the time it stops1 you    
find the liquid in which this matter has
 been formed has become altered in its  
quality4 ,to begin with it was a mere   
sweetish substance1 having the flavour  
of whatever might be the plant from     
which it was expressed1 or having merely
 the taste and the absence of smell of a
 solution of sugar2 but by the time that
 this change that ,i have been briefly  
describing to you is accomplished the   
liquid has become completely altered1 it
 has acquired a peculiar smell1 and1    
what is still more remarkable1 it has   
gained the property of intoxicating the 
person who drinks it4 ,nothing can be   
more innocent than a solution of sugar2 
nothing can be less innocent1 if taken  
in excess1 as you all know1 than those  
fermented matters which are produced    
from sugar4 ,well1 again1 if you notice 
that bubbling1 or1 as it were1 seething 
of the liquid1 which has accompanied the
 whole of this process1 you will find   

that it is produced by the evolution of 
little bubbles of air-like substance out
 of the liquid2 and ,i dare say you all 
know this air-like substance is not like
 common air2 it is not a substance which
 a man can breathe with impunity4 ,you  
often hear of accidents which take place
 in brewers' vats when men go in        
carelessly1 and get suffocated there    
without knowing that there was anything 
evil awaiting them4 ,and if you tried   
the experiment with this liquid ,i am   
telling of while it was fermenting1 you 
would find that any small animal let    
down into the vessel would be similarly 
stifled2 and you would discover that a  
light lowered down into it would go out4
 ,well1 then1 lastly1 if after this     
liquid has been thus altered you expose 
it to that process which is called      
distillation2 that is to say1 if you put
 it into a still1 and collect the       
matters which are sent over1 you obtain1
 when you first heat it1 a clear        
transparent liquid1 which1 however1 is  

something totally different from water2 
it is much lighter2 it has a strong     
smell1 and it has an acrid taste2 and it
 possesses the same intoxicating power  
as the original liquid1 but in a much   
more intense degree4 ,if you put a light
 to it1 it burns with a bright flame1   
and it is that substance which we know  
as spirits of wine4  ,now these facts   
which ,i have just put before you--all  
but the last--have been known from      
extremely remote antiquity4 ,it is1 ,i  
hope one of the best evidences of the   
antiquity of the human race1 that among 
the earliest records of all kinds of    
men1 you find a time recorded when they 
got drunk4 ,we may hope that that must  
have been a very late period in their   
history4 ,not only have we the record of
 what happened to ,noah1 but if we turn 
to the traditions of a different people1
 those forefathers of ours who lived in 
the high lands of ,northern ,india1 we  
find that they were not less addicted to
 intoxicating liquids2 and ,i have no   

doubt that the knowledge of this process
 extends far beyond the limits of       
historically recorded time4 ,and it is a
 very curious thing to observe that all 
the names we have of this process1 and  
all that belongs to it1 are names that  
have their roots not in our present     
language1 but in those older languages  
which go back to the times at which this
 country was peopled4 ,that word        
fermentation for example1 which is the  
title we apply to the whole process1 is 
a ,latin term2 and a term which is      
evidently based upon the fact of the    
effervescence of the liquid4 ,then the  
,french1 who are very fond of calling   
themselves a ,latin race1 have a        
particular word for ferment1 which is   
'levure'4 ,and1 in the same way1 we have
 the word leaven1 those two words having
 reference to the heaving up1 or to the 
raising of the substance which is       
fermented4 ,now those are words which we
 get from what ,i may call the ,latin   
side of our parentage2 but if we turn to

 the ,saxon side1 there are a number of 
names connected with this process of    
fermentation4 ,for example1 the ,germans
 call fermentation--and the old ,germans
 did so--gahren2 and they call anything 
which is used as a ferment by such      
names1 such as gheist and geest1 and    
finally in low ,german1 yest2 and that  
word you know is the word our ,saxon    
forefathers used1 and is almost the same
 as the word which is commonly employed 
in this country to denote the common    
ferment of which ,i have been speaking4 
,so they have another name1 the word    
hefe1 which is derived from their verb  
heben1 which signifies to raise up2 and 
they have yet a third name1 which is    
also one common in this country 7,i do  
not know whether it is common in        
,lancashire1 but it is certainly very   
common in the ,midland countries71 the  
word barm1 which is derived from a root 
which signifies to raise or to bear up4 
,barm is a something borne up2 and thus 
there is much more real relation than is

 commonly supposed by those who make    
puns1 between the beer which a man takes
 down his throat and the bier upon which
 that process1 if carried to excess1    
generally lands him1 for they are both  
derived from the root signifying bearing
 up2 the one thing is borne upon men's  
shoulders1 and the other is the         
fermented liquid which was borne up by  
the fermentation taking place in itself4
  ,again1 ,i spoke of the produce of    
fermentation as spirit of wine4 ,now    
what a very curious phrase that is1 if  
you come to think of it4 ,the old       
alchemists talked of the finest essence 
of anything as if it had the same sort  
of relation to the thing itself as a    
man's spirit is supposed to have to his 
body2 and so they spoke of this fine    
essence of the fermented liquid as being
 the spirit of the liquid4 ,thus came   
about that extraordinary ambiguity of   
language1 in virtue of which you apply  
precisely the same substantive name to  
the soul of man and to a glass of gin6  

,and then there is still yet one other  
most curious piece of nomenclature      
connected with this matter1 and that is 
the word alcohol itself1 which is now so
 familiar to everybody4 ,alcohol        
originally meant a very fine powder4    
,the women of the ,arabs and other      
,eastern people are in the habit of     
tinging their eyelashes with a very fine
 black powder which is made of antimony1
 and they call that kohol2 and the al is
 simply the article put in front of it1 
so as to say the kohol4 ,and up to the  
#agth century in this country the word  
alcohol was employed to signify any very
 fine powder2 you find it in ,robert    
,boyle's works that he uses alcohol for 
a very fine subtle powder4 ,but then    
this name of anything very fine and very
 subtle came to be specially connected  
with the fine and subtle spirit obtained
 from the fermentation of sugar2 and ,i 
believe that the first person who fairly
 fixed it as the proper name of what we 
now commonly call spirits of wine1 was  

the great ,french chemist ,lavoisier1 so
 comparatively recent is the use of the 
word alcohol in this specialised sense4 
,so much by way of general introduction 
to the subject on which ,i have to speak
 to-night4 ,what ,i have hitherto stated
 is simply what we may call common      
knowledge1 which everybody may acquaint 
himself with4 ,and you know that what we
 call scientific knowledge is not any   
kind of conjuration1 as people sometimes
 suppose1 but it is simply the          
application of the same principles of   
common sense that we apply to common    
knowledge1 carried out1 if ,i may so    
speak1 to knowledge which is uncommon4  
,and all that we know now of this       
substance1 yeast1 and all the very      
strange issues to which that knowledge  
has led us1 have simply come out of the 
inveterate habit1 and a very fortunate  
habit for the human race it is1 which   
scientific men have of not being content
 until they have routed out all the     
different chains and connections of     

apparently simple phenomena1 until they 
have taken them to pieces and understood
 the conditions upon which they depend4 
,i will try to point out to you now what
 has happened in consequence of         
endeavouring to apply this process of   
analysis1 as we call it1 this teazing   
out of an apparently simple fact into   
all the little facts of which it is made
 up1 to the ascertained facts relating  
to the barm or the yeast2 secondly1 what
 has come of the attempt to ascertain   
distinctly what is the nature of the    
products which are produced by          
fermentation2 then what has come of the 
attempt to understand the relation      
between the yeast and the products2 and 
lastly1 what very curious side issues if
 ,i may so call them--have branched out 
in the course of this inquiry1 which has
 now occupied somewhere about two       
centuries4  ,the first thing was to make
 out precisely and clearly what was the 
nature of this substance1 this          
apparently mere scum and mud that we    

call yeast4 ,and that was first         
commenced seriously by a wonderful old  
,dutchman of the name of ,leeuwenhoek1  
who lived some two hundred years ago1   
and who was the first person to invent  
thoroughly trustworthy microscopes of   
high powers4 ,now1 ,leeuwenhoek went to 
work upon this yeast mud1 and by        
applying to it high powers of the       
microscope1 he discovered that it was no
 mere mud such as you might at first    
suppose1 but that it was a substance    
made up of an enormous multitude of     
minute grains1 each of which had just as
 definite a form as if it were a grain  
of corn1 although it was vastly smaller1
 the largest of these not being more    
than the two-thousandth of an inch in   
diameter2 while1 as you know1 a grain of
 corn is a large thing1 and the very    
smallest of these particles were not    
more than the seven-thousandth of an    
inch in diameter4 ,leeuwenhoek saw that 
this muddy stuff was in reality a       
liquid1 in which there were floating    

this immense number of definitely shaped
 particles1 all aggregated in heaps and 
lumps and some of them separate4 ,that  
discovery remained1 so to speak1 dormant
 for fully a century1 and then the      
question was taken up by a ,french      
discoverer1 who1 paying great attention 
and having the advantage of better      
instruments than ,leeuwenhoek had1      
watched these things and made the       
astounding discovery that they were     
bodies which were constantly being      
reproduced and growing2 than when one of
 these rounded bodies was once formed   
and had grown to its full size1 it      
immediately began to give off a little  
bud from one side1 and then that bud    
grew out until it had attained the full 
size of the first1 and that1 in this    
way1 the yeast particle was undergoing a
 process of multiplication by budding1  
just as effectual and just as complete  
as the process of multiplication of a   
plant by budding2 and thus this         
,frenchman1 ,cagniard de la ,tour1      

arrived at the conclusion--very         
creditable to his sagacity1 and which   
has been confirmed by every observation 
and reasoning since--that this          
apparently muddy refuse was neither more
 nor less than a mass of plants1 of     
minute living plants1 growing and       
multiplying in the sugary fluid in which
 the yeast is formed4 ,and from that    
time forth we have known this substance 
which forms the scum and the lees as the
 yeast plant2 and it has received a     
scientific name--which ,i may use       
without thinking of it1 and which ,i    
will therefore give you--namely1        
,torula4 ,well1 this was a capital      
discovery4 ,the next thing to do was to 
make out how this torula was related to 
the other plants4 ,i won't weary you    
with the whole course of investigation1 
but ,i may sum up its results1 and they 
are these--that the torula is a         
particular kind of a fungus1 a          
particular state rather1 of a fungus or 
mould4 ,there are many moulds which     

under certain conditions give rise to   
this torula condition1 to a substance   
which is not distinguishable from yeast1
 and which has the same properties as   
yeast--that is to say1 which is able to 
decompose sugar in the curious way that 
we shall consider by-and-by4 ,so that   
the yeast plant is a plant belonging to 
a group of the ,fungi1 multiplying and  
growing and living in this very         
remarkable manner in the sugary fluid   
which is1 so to speak1 the nidus or home
 of the yeast4  ,that1 in a few words1  
is1 as far as investigation--by the help
 of one's eye and by the help of the    
microscope--has taken us4 ,but now there
 is an observer whose methods of        
observation are more refined than those 
of men who use their eye1 even though it
 be aided by the microscope2 a man who  
sees indirectly further than we can see 
directly--that is1 the chemist2 and the 
chemist took up this question1 and his  
discovery was not less remarkable than  
that of the microscopist4 ,the chemist  

discovered that the yeast plant being   
composed of a sort of bag1 like a       
bladder1 inside which is a peculiar     
soft1 semifluid material--the chemist   
found that this outer bladder has the   
same composition as the substance of    
wood1 that material which is called     
cellulose1 and which consists of the    
elements carbon and hydrogen and oxygen1
 without any nitrogen4 ,but then he also
 found 7the first person to discover it 
was an ,italian chemist1 named ,fabroni1
 in the end of the last century7 that   
this inner matter which was contained in
 the bag1 which constitutes the yeast   
plant1 was a substance containing the   
elements carbon and hydrogen and oxygen 
and nitrogen2 that it was what ,fabroni 
called a vegeto-animal substance1 and   
that it had the peculiarities of what   
are commonly called animal products4    
,this again was an exceedingly          
remarkable discovery4 ,it lay neglected 
for a time1 until it was subsequently   
taken up by the great chemists of modern

 times1 and they1 with their delicate   
methods of analysis1 have finally       
decided that1 in all essential respects1
 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 muscles1
 which forms the chief part of our own  
blood1 which forms the chief part of the
 white of the egg2 that1 in fact1       
although this little organism is a      
plant1 and nothing but a plant1 yet that
 its active living contents contain a   
substance which is called protein1 which
 is of the same nature as the substance 
which forms the foundation of every     
animal organism whatever4  ,now we come 
next to the question of the analysis of 
the products1 of that which is produced 
during the process of fermentation4 ,so 
far back as the beginning of the #afth  
century1 in the times of transition     
between the old alchemy and the modern  
chemistry1 there was a remarkable man1  
,von ,helmont1 a ,dutchman1 who saw the 

difference between the air which comes  
out of a vat where something is         
fermenting and common air4 ,he was the  
man who invented the term gas1 and he   
called this kind of gas gas             
silvestre--so to speak gas that is wild1
 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       
cellars4 ,then1 the gradual process of  
investigation going on1 it was          
discovered that this substance1 then    
called fixed air1 was a poisonous gas1  
and it was finally identified with that 
kind of gas which is obtained by burning
 charcoal in the air1 which is called   
carbonic acid4 ,then the substance      
alcohol was subjected to examination1   
and it was found to be a combination of 
carbon1 and hydrogen1 and oxygen4 ,then 
the sugar which was contained in the    
fermenting liquid was examined and that 
was found to contain the three elements 
carbon1 hydrogen1 and oxygen4 ,so that  

it was clear there were in sugar the    
fundamental elements which are contained
 in the carbonic acid1 and in the       
alcohol4 ,and then came that great      
chemist ,lavoisier1 and he examined into
 the subject carefully1 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    
lost1 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        
fermentation4 ,he thought he discovered 
that the whole weight of the sugar was  
represented by the carbonic acid        
produced2 that in other words1 supposing
 this tumbler to represent the sugar1   
that the action of fermentation was as  
it were the splitting of it1 the one    
half going away in the shape of carbonic
 acid1 and the other half going away in 
the shape of alcohol4 ,subsequent       
inquiry1 careful research with the      

refinements of modern chemistry1 have   
been applied to this problem1 and they  
have shown that ,lavoisier was not quite
 correct2 that what he says is quite    
true for about #ie per cent4 of the     
sugar1 but that the other #e per cent41 
or nearly so1 is converted into two     
other things2 one of them1 matter which 
is called succinic acid1 and the other  
matter which is called glycerine1 which 
you all know now as one of the commonest
 of household matters4 ,it may be that  
we have not got to the end of this      
refined analysis yet1 but at any rate1  
,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 #ii per cent4 at
 least of the sugar1 and that #ii per   
cent4 is split up into these four       
things1 carbonic acid1 alcohol1 succinic
 acid1 and glycerine4 ,so that it may be
 that none of the sugar whatever        

disappears1 and that only its parts1 so 
to speak1 are re-arranged1 and if any of
 it disappears1 certainly it is a very  
small portion4  ,now these are the facts
 of the case4 ,there is the fact of the 
growth of the yeast plant2 and there is 
the fact of the splitting up of the     
sugar4 ,what relation have these two    
facts to one another8  ,for a very long 
time that was a great matter of dispute4
 ,the early ,french observers1 to do    
them justice1 discerned the real state  
of the case1 namely1 that there was a   
very close connection between the actual
 life of the yeast plant and this       
operation of the splitting up of the    
sugar2 and that one was in some way or  
other connected with the other4 ,all    
investigation subsequently has confirmed
 this original idea4 ,it has been shown 
that if you take any measures by which  
other plants of like kind to the torula 
would be killed1 and by which the yeast 
plant is killed1 then the yeast loses   
its efficiency4 ,but a capital          

experiment upon this subject was made by
 a very distinguished man1 ,helmholz1   
who performed an experiment of this     
kind4 ,he had two vessels--one of them  
we will suppose full of yeast1 but over 
the bottom of it1 as this might be1 was 
tied a thin film of bladder2            
consequently1 through that thin film of 
bladder all the liquid parts of the     
yeast would go1 but the solid parts     
would be stopped behind2 the torula     
would be stopped1 the liquid parts of   
the yeast would go4 ,and then he took   
another vessel containing a fermentable 
solution of sugar1 and he put one inside
 the other2 and in this way you see the 
fluid parts of the yeast were able to   
pass through with the utmost ease into  
the sugar1 but the solid parts could not
 get through at all4 ,and he judged     
thus3 if the fluid parts are those which
 excite fermentation1 then1 inasmuch as 
these are stopped1 the sugar will not   
ferment2 and the sugar did not ferment1 
showing quite clearly1 that an immediate

 contact with the solid1 living torula  
was absolutely necessary to excite this 
process of splitting up of the sugar4   
,this experiment was quite conclusive as
 to this particular point1 and has had  
very great fruits in other directions4  
,well1 then1 the yeast plant being      
essential to the production of          
fermentation1 where does the yeast plant
 come from8 ,here1 again1 was another   
great problem opened up1 for1 as ,i said
 at starting1 you have1 under ordinary  
circumstances in warm weather1 merely to
 expose some fluid containing a solution
 of sugar1 or any form of syrup or      
vegetable juice to the air1 in order1   
after a comparatively short time1 to see
 all these phenomena of fermentation4   
,of course the first obvious suggestion 
is1 that the torula has been generated  
within the fluid4 ,in fact1 it seems at 
first quite absurd to entertain any     
other conviction2 but that belief would 
most assuredly be an erroneous one4     
,towards the beginning of this century1 

in the vigorous times of the old ,french
 wars1 there was a ,monsieur ,appert1   
who had his attention directed to the   
preservation of things that ordinarily  
perish1 such as meats and vegetables1   
and in fact he laid the foundation of   
our modern method of preserving meats2  
and he found that if he boiled any of   
these substances and then tied them so  
as to exclude the air1 that they would  
be preserved for any time4 ,he tried    
these experiments1 particularly with the
 must of wine and with the wort of beer2
 and he found that if the wort of beer  
had been carefully boiled and was       
stopped in such a way that the air could
 not get at it1 it would never ferment4 
,what was the reason of this8 ,that1    
again1 became the subject of a long     
string of experiments1 with this        
ultimate result1 that if you take       
precautions to prevent any solid matters
 from getting into the must of wine or  
the wort of beer1 under these           
circumstances--that is to say1 if the   

fluid has been boiled and placed in a   
bottle1 and if you stuff the neck of the
 bottle full of cotton wool1 which      
allows the air to go through and stops  
anything of a solid character however   
fine1 then you may let it be for ten    
years and it will not ferment4 ,but if  
you take that plug out and give the air 
free access1 then1 sooner or later      
fermentation will set up4 ,and there is 
no doubt whatever that fermentation is  
excited only by the presence of some    
torula or other1 and that that torula   
proceeds in our present experience1 from
 pre-existing torulae4 ,these little    
bodies are excessively light4 ,you can  
easily imagine what must be the weight  
of little particles1 but slightly       
heavier than water1 and not more than   
the two-thousandth or perhaps           
seven-thousandth of an inch in diameter4
 ,they are capable of floating about and
 dancing like motes in the sunbeam2 they
 are carried about by all sorts of      
currents of air2 the great majority of  

them perish2 but one or two1 which may  
chance to enter into a sugary solution1 
immediately enter into active life1 find
 there the conditions of their          
nourishment1 increase and multiply1 and 
may give rise to any quantity whatever  
of this substance yeast4 ,and1 whatever 
may be true or not be true about this   
spontaneous generation1 as it is called 
in regard to all other kinds of living  
things1 it is perfectly certain1 as     
regards yeast1 that it always owes its  
origin to this process of transportation
 or inoculation1 if you like so to call 
it1 from some other living yeast        
organism2 and so far as yeast is        
concerned1 the doctrine of spontaneous  
generation is absolutely out of court4  
,and not only so1 but the yeast must be 
alive in order to exert these peculiar  
properties4 ,if it be crushed1 if it be 
heated so far that its life is          
destroyed1 that peculiar power of       
fermentation is not excited4 ,thus we   
have come to this conclusion1 as the    

result of our inquiry1 that the         
fermentation of sugar1 the splitting of 
the sugar into alcohol and carbonic     
acid1 glycerine1 and succinic acid1 is  
the result of nothing but the vital     
activity of this little fungus1 the     
torula4  ,and now comes the further     
exceedingly difficult inquiry--how is it
 that this plant1 the torula1 produces  
this singular operation of the splitting
 up of the sugar8 ,fabroni1 to whom ,i  
referred some time ago1 imagined that   
the effervescence of fermentation was   
produced in just the same way as the    
effervescence of a sedlitz powder1 that 
the yeast was a kind of acid1 and that  
the sugar was a combination of carbonic 
acid and some base to form the alcohol1 
and that the yeast combined with this   
substance1 and set free the carbonic    
acid2 just as when you add carbonate of 
soda to acid you turn out the carbonic  
acid4 ,but of course the discovery of   
,lavoisier that the carbonic acid and   
the alcohol taken together are very     

nearly equal in weight to the sugar1    
completely upset this hypothesis4       
,another view was therefore taken by the
 ,french chemist1 ,thenard1 and it is   
still held by a very eminent chemist1   
,m4 ,pasteur1 and their view is this1   
that the yeast1 so to speak1 eats a     
little of the sugar1 turns a little of  
it to its own purposes1 and by so doing 
gives such a shape to the sugar that the
 rest of it breaks up into carbonic acid
 and alcohol4  ,well1 then1 there is a  
third hypothesis1 which is maintained by
 another very distinguished chemist1    
,liebig1 which denies either of the     
other two1 and which declares that the  
particles of the sugar are1 as it were1 
shaken asunder by the forces at work in 
the yeast plant4 ,now ,i am not going to
 take you into these refinements of     
chemical theory1 ,i cannot for a moment 
pretend to do so1 but ,i may put the    
case before you by an analogy4 ,suppose 
you compare the sugar to a card house1  
and suppose you compare the yeast to a  

child coming near the card house1 then  
,fabroni's hypothesis was that the child
 took half the cards away2 ,thenard's   
and ,pasteur's hypothesis is that the   
child pulls out the bottom card and thus
 makes it tumble to pieces2 and         
,liebig's hypothesis is that the child  
comes by and shakes the table and       
tumbles the house down4 ,i appeal to my 
friend here 7,professor ,roscoe7 whether
 that is not a fair statement of the    
case4  ,having thus1 as far as ,i can1  
discussed the general state of the      
question1 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 yeast4 ,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 wood1   
and of an interior semifluid mass which 
contains a substance1 identical in its  
composition1 in a broad sense1 with that
 which constitutes the flesh of animals4

 ,subsequently1 after the structure of  
the yeast plant had been carefully      
observed1 it was discovered that all    
plants1 high and low1 are made up of    
separate bags or cells1 as they are     
called2 these bags or cells having the  
composition of the pure matter of wood2 
having the same composition1 broadly    
speaking1 as the sac of the yeast plant1
 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 plant4 ,and      
therefore this remarkable result came   
out--that however much a plant may      
differ from an animal1 yet that the     
essential constituent of the contents of
 these various cells or sacs of which   
the plant is made up1 the nitrogenous   
protein matter1 is the same in the      
animal as in the plant4 ,and not only   
was this gradually discovered1 but it   
was found that these semifluid contents 
of the plant cell had1 in many cases1 a 
remarkable power of contractility quite 

like that of the substance of animals4  
,and about #bd or #be years ago1 namely1
 about the year #ahdf1 to the best of my
 recollection1 a very eminent ,german   
botanist1 ,hugo ,von ,mohl1 conferred   
upon this substance which is found in   
the interior of the plant cell1 and     
which is identical with the matter found
 in the inside of the yeast cell1 and   
which again contains an animal substance
 similar to that of which we ourselves  
are made up--he conferred upon this that
 title of protoplasm1 which has brought 
other people a great deal of trouble    
since6 ,i beg particularly to say that1 
because ,i find many people suppose that
 ,i was the inventor of that term1      
whereas it has been in existence for at 
least twenty-five years4 ,and then other
 observers1 taking the question up1 came
 to this astonishing conclusion 7working
 from this basis of the yeast71 that the
 differences between animals and plants 
are not so much in the fundamental      
substances which compose them1 not in   

the protoplasm1 but in the manner in    
which the cells of which their bodies   
are built up have become modified4      
,there is a sense in which it is        
true--and the analogy was pointed out   
very many years ago by some ,french     
botanists and chemists--there is a sense
 in which it is true that every plant is
 substantially an enormous aggregation  
of bodies similar to yeast cells1 each  
having to a certain extent its own      
independent life4 ,and there is a sense 
in which it is also perfectly           
true--although it would be impossible   
for me to give the statement to you with
 proper qualifications and limitations  
on an occasion like this--but there is  
also a sense in which it is true that   
every animal body is made up of an      
aggregation of minute particles of      
protoplasm1 comparable each of them to  
the individual separate yeast plant4    
,and those who are acquainted with the  
history of the wonderful revolution     
which has been worked in our whole      

conception of these matters in the last 
thirty years1 will bear me out in saying
 that the first germ of them1 to a very 
great extent1 was made to grow and      
fructify by the study of the yeast      
plant1 which presents us with living    
matter in almost its simplest condition4
  ,then there is yet one last and most  
important bearing of this yeast         
question4 ,there is one direction       
probably in which the effects of the    
careful study of the nature of          
fermentation will yield results more    
practically valuable to mankind than any
 other4 ,let me recall to your minds the
 fact which ,i stated at the beginning  
of this lecture4 ,suppose that ,i had   
here a solution of pure sugar with a    
little mineral matter in it2 and suppose
 it were possible for me to take upon   
the point of a needle one single1       
solitary yeast cell1 measuring no more  
perhaps than the three-thousandth of an 
inch in diameter--not bigger than one of
 those little coloured specks of matter 

in my own blood at this moment1 the     
weight of which it would be difficult to
 express in the fraction of a grain--and
 put it into this solution4 ,from that  
single one1 if the solution were kept at
 a fair temperature in a warm summer's  
day1 there would be generated1 in the   
course of a week1 enough torulae to form
 a scum at the top and to form lees at  
the bottom1 and to change the perfectly 
tasteless and entirely harmless fluid1  
syrup1 into a solution impregnated with 
the poisonous gas carbonic acid1        
impregnated with the poisonous substance
 alcohol2 and that1 in virtue of the    
changes worked upon the sugar by the    
vital activity of these infinitesimally 
small plants4 ,now you see that this is 
a case of infection4 ,and from the time 
that the phenomenon of fermentation were
 first carefully studied1 it has        
constantly been suggested to the minds  
of thoughtful physicians that there was 
a something astoundingly similar between
 this phenomena of the propagation of   

fermentation by infection and contagion1
 and the phenomena of the propagation of
 diseases by infection and contagion4   
,out of this suggestion has grown that  
remarkable theory of many diseases which
 has been called the germ theory of     
disease1 the idea1 in fact1 that we owe 
a great many diseases to particles      
having a certain life of their own1 and 
which are capable of being transmitted  
from one living being to another1       
exactly as the yeast plant is capable of
 being transmitted from one tumbler of  
saccharine substance to another4 ,and   
that is a perfectly tenable hypothesis1 
one which in the present state of       
medicine ought to be absolutely         
exhausted and shown not to be true1     
until we take to others which have less 
analogy in their favour4 ,and there are 
some diseases most assuredly in which it
 turns out to be perfectly correct4     
,there are some forms of what are called
 malignant carbuncle which have been    
shown to be actually effected by a sort 

of fermentation1 if ,i may use the      
phrase1 by a sort of disturbance and    
destruction of the fluids of the animal 
body1 set up by minute organisms which  
are the cause of this destruction and of
 this disturbance2 and only recently the
 study of the phenomena which accompany 
vaccination has thrown an immense light 
in this direction1 tending to show by   
experiments of the same general         
character as that to which ,i referred  
as performed by ,helmholz1 that there is
 a most astonishing analogy between the 
contagion of that healing disease and   
the contagion of destructive diseases4  
,for it has been made out quite clearly1
 by investigations carried on in ,france
 and in this country1 that the only part
 of the vaccine matter which is         
contagious1 which is capable of carrying
 on its influence in the organism of the
 child who is vaccinated1 is the solid  
particles and not the fluid4 ,by        
experiments of the most ingenious kind1 
the solid parts have been separated from

 the fluid parts1 and it has then been  
discovered that you may vaccinate a     
child as much as you like with the fluid
 parts1 but no effect takes place1      
though an excessively small portion of  
the solid particles1 the most minute    
that can be separated1 is amply         
sufficient to give rise to all the      
phenomena of the cow pock1 by a process 
which we can compare to nothing but the 
transmission of fermentation from one   
vessel into another1 by the transport to
 the one of the torula particles which  
exist in the other4 ,and it has been    
shown to be true of some of the most    
destructive diseases which infect       
animals1 such diseases as the sheep pox1
 such diseases as that most terrible and
 destructive disorder of horses1        
glanders1 that in these1 also1 the      
active power is the living solid        
particle1 and that the inert part is the
 fluid4 ,however1 do not suppose that ,i
 am pushing the analogy too far4 ,i do  
not mean to say that the active1 solid  

parts in these diseased matters are of  
the same nature as living yeast plants2 
but1 so far as it goes1 there is a most 
surprising analogy between the two2 and 
the value of the analogy is this1 that  
by following it out we may some time or 
other come to understand how these      
diseases are propagated1 just as we     
understand1 now1 about fermentation2 and
 that1 in this way1 some of the greatest
 scourges which afflict the human race  
may be1 if not prevented1 at least      
largely alleviated4  ,this is the       
conclusion of the statements which ,i   
wished to put before you4 ,you see we   
have not been able to have any          
accessories4 ,if you will come in such  
numbers to hear a lecture of this kind1 
all ,i can say is1 that diagrams cannot 
be made big enough for you1 and that it 
is not possible to show any experiments 
illustrative of a lecture on such a     
subject as ,i have to deal with4 ,of    
course my friends the chemists and      
physicists are very much better off1    

because they can not only show you      
experiments1 but you can smell them and 
hear them6 ,but in my case such aids are
 not attainable1 and therefore ,i have  
taken a simple subject and have dealt   
with it in such a way that ,i hope you  
all understand it1 at least so far as ,i
 have been able to put it before you in 
words2 and having once apprehended such 
of the ideas and simple facts of the    
case as it was possible to put before   
you1 you can see for yourselves the     
great and wonderful issues of such an   
apparently homely subject4