12 -MITSCHERLICH ON CHEMICAL REACTIONS 
measure of carbonic acid there is formed one measure of alcohol ; 
but, according to the kind of sugar which undergoes fermenta- 
tion, an elimination or a fixation of water takes place. The first 
is the case with glucose; the second with the variety of sugar 
soluble in alcohol. The body which determines this action, the 
only one by means of which it is capable of being produced, is 
an organized body. 
Without entering into the detail of the opinions to which this 
phenomenon has given rise, we may discuss the facts, which 
alone have an interest in this question. Ferment is composed 
of oval and round globules; these globules are large enough to 
be retained by filtering paper. If a small quantity of yeast is 
put into a tube closed at one end by some bibulous paper, and 
this is then introduced into a solution of sugar, the latter passes 
through the pores of the paper and undergoes alcoholic fermenta- 
tion, but only in the tube which contains the yeast. The fermen- 
tation takes place in the solution of sugar in which the tube is 
placed, only after a shorter or longer time, and always under the 
influence of the globules of yeast, which in the end pass through 
the pores of the paper, which softens by prolonged contact with 
the liquid. This experiment proves satisfactorily that the fer- 
mentation takes place only at the surface of the globules of yeast. 
I have also instituted other experiments, which prove what I 
have just said. M. Schwann, on his part, has also made some ; 
but they are not so decisive as those which I have just related. 
I have never observed fermentation without globules of yeast, 
and the phenomenon is effected always at the surface of the 
latter. 
We require only 1 per cent. of globules of yeast to effect the 
complete transformation of sugar into alcohol and carbonic acid ; 
and when perfectly organized globules are taken, they undergo 
scarcely any change during the fermentation; they no longer 
effect it when they are destroyed. On putting them in contact 
with bodies which have the property of arresting fermentation, 
they are seen, when examined with a microscope, to contract at 
the very instant when these touch them. 
Globules of yeast, then, in presence of sugar or of sugar and 
water, which contain the elements of carbonic acid and alcohol, 
act precisely as platinum sponge with regard to oxygenated water. 
Naturalists who have engaged in the study of the most simple 
organized bodies, assert that the globules of yeastshould beclassed 
