404 THE BEGINNINGS OF LIFE. 



But since the discovery by Cagniard-Latour and 

 Schwann, in 1836, of the yeast-plant, which invariably 

 reveals itself during the vinous fermentation; and 

 since the recognition of the existence of a similar 

 relationship between other fermentations and other 

 organisms, there have always been persons who have 

 inclined to the notion that the associated organism 

 was the actual cause of the fermentation itself. For 

 three or four years after the discovery of the yeast- 

 plant, it was warmly advocated by Cagniard-Latour, 

 Turpin, Mitscherlich, and others, that living organisms 

 alone were capable of initiating the changes known 

 as fermentations that they, in fact, were the only 

 true ferments. According to the notions of Liebig, 

 Gerhardt, and others, fermentations are separated by 

 no hard and fast line from chemical changes in general ; 

 here, however, a limitation was sought to be established ; 

 a hard and fast line was to be drawn, and fermentations 

 were to be supposed to differ from chemical changes in 

 general, by the fact that they could only be initiated 

 by the presence and influence of living organisms. 

 Such a limitation seemed of itself to necessitate the 

 supposition that the chemical changes occurring in 

 living things were wholly different from all other che- 

 mical changes that the changes, in fact, constituting 

 fermentations were initiated by occult c vital ' influ- 

 ences.' This is the doctrine which M. Pasteur has 

 revived, and which he has sought to establish upon a 

 firm foundation. He says: c je trouvais que toutes 



