ON THE NATURE OF FERMENTATION 339 
the yeast plant, and commonly endowed with a remarkable power of locomotion. 
I say that, in the putrefying blood, we find these organisms developing pari 
passu with the fermentation. 
Now, the question is, Are these bacteria the cause of the putrefactive 
fermentation, or are they merely accidental concomitants ? These are two 
views which are entertained at the present day by men of high eminence. It 
may be said, ‘ Why should there be any doubt that the bacteria are the cause 
of the putrefactive fermentation, any more than there is a doubt that the Torula 
Cerevisiae is the cause of the alcoholic?’ Well, one reason I believe to be that 
the bacteria are so exceedingly small. They are not so easily defined as the 
yeast plant. We cannot get them in a mass as we can get a mass of yeast ; 
at least without a great deal of trouble ; and, besides that, they occur very 
similar in appearance in a great number of different fermentations. There is, 
therefore, so far some colour for doubting whether bacteria are the cause of 
a special fermentation, like this putrefaction. Then there is another ground 
justifying such a view; for certain it is that organic substances are lable to 
extremely remarkable alterations, decompositions, under the influence of agents 
which are endowed with no life at all. As good an example of this as we can 
take is what occurs in the bitter almond when it 1s bruised with water. You 
all know what takes place under those circumstances; that there is prussic 
acid developed, and essential oil of almonds, with other materials. Now, these 
did not exist beforehand in the almond, but they are the result of the mutual 
action upon each other of two constituents, neither of which was hydrocyanic 
acid nor oil of bitter almonds, &c. These two constituents are termed emulsin 
and amygdalin. Amygdalin can be got from the almond in the form of definite 
crystals ; and emulsin, though not a crystallizable substance, but a variety 
of albumen, can also be obtained separate. Till these two materials are in 
a state of solution in water, they do not act upon each other at all; but, as 
soon as they are in watery solution, the emulsin so acts upon the amygdalin 
that the latter becomes broken up into the constituents to which I have referred. 
This is an exceedingly remarkable fact. Undoubtedly, the emulsin is dead ; 
there is nothing living about it. It is not an organism. It is obtained by a 
process of alcoholic extraction, and so forth. It is thoroughly a chemical sub- 
stance, a merely dead substance, if we may so speak, and yet it does produce 
this remarkable effect upon the amygdalin. But, when we come to consider 
this case, we find that the process, remarkable as it is, lacks the true character 
of genuine fermentation, that of the faculty of self-propagation of the ferment. 
Liebig himself, who was the great advocate of the doctrine of so-called chemical! 
ferments, and who, along with Wohler, discovered this action of emulsin on 
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