84 THE PLACE OF SCIENCE IN 
very soon satisfied himself that the process of fermentation 
was connected in some way with the life and growth of 
yeast plant. And when he had established that, he had to 
decide the question as to the access of the yeast to the liquor 
which underwent fermentation. In many cases it was deliber- 
ately added. In some cases it was not added. In order 
to make wine, all that is necessary is to take the grape, 
crush it, and then the liquor undergoes fermentation and 
alcohol is produced. Whence comes yeast, no one knew. 
It was thought it came from nowhere in particular. But 
Pasteur, early in his career, formed a strong prejudice against 
the view that living things can come into existence without 
parentage, and he expected that wherever fermentation 
occurred the yeast somehow must have come in from outside. — 
The process of fermentation is akin to putrefaction and the 
connexion between the two was easily discerned by Pasteur. 
In liquids undergoing putrefaction Pasteur found organisms 
not unlike those which occurred in fermenting liquor, and 
studying the process he came to the conclusion that putre- 
faction, like fermentation, depended upon the access to the 
liquids of organisms from an outside source. The only other 
explanation was that the organisms were generated in the 
liquid within which life did not previously exist. So Pasteur 
was led to take up the question whether life ever came into 
existence in the world without parentage, a view which 
nowadays may seem remarkable and utterly unacceptable, 
but which in those days, not very remote—I am speaking 
of a time well within my own memory—seemed to be almost 
a matter of course and a matter of nosurprise. Then Pasteur 
began to try and find out whether the germs that cause 
fermentation and putrefaction came, as he supposed, from 
outside. And he found that the germs did come from out- 
side, and so he founded the science of bacteriology. He 
showed that if means were taken to use materials which in 
