44 LOUIS PASTEUR. 



come so fruitful. One of the ferments most in use, 

 and known as early as the leavening of dough or the 

 turning of milk, is the deposit formed in beer barrels, 

 which is commonly called yeast. Repeating an obser- 

 vation of the naturalist Leuwenhoeck, Cagniard- 

 Latour saw this yeast, which was composed of cells, 

 multiplying itself by budding, and he proposed to him- 

 self the question whether the fermentation of sugar 

 was not connected with this act of cellular vegeta- 

 tion. But as in other fermentations the existence 

 of an organism had not been observed even by the 

 most careful search, the hypothesis of Cagniard-Latour 

 of a possible relation between the organisation of the 

 ferment and the property of being a ferment was 

 abandoned, though not without regret by some 

 physiologists. M. Dumas, for example, recognised 

 that in the budding of the yeast globules there must 

 be some clue to the phenomenon of fermentation. I, 

 however, repeat that as nothing of the kind had bsen 

 found elsewhere, and as all other fermentations pre- 

 sented the common character of requiring, to put them 

 in train, organic matter in a state of decomposition, 

 the hypothesis of Cagniard-Latour remained a simple 

 incident, instead of having the value of a scientific 

 principle. 



Liebig, moreover, carrying general opinion along 

 with him, contended that it is not because of its 

 being organised that yeast is active, but because of its 



