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 no surprise. 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 



