250 THE FLOATING-MATTER OF THE AIR. 



ordinary alcoholic leaven be found. As previously 

 proved by Lechartier and Bellamy, the fermentation 

 was the work of the living cells of the fruit itself, after 

 air had been denied to them. When, moreover, the cells 

 were destroyed by bruising, no fermentation ensued. 

 The fermentation was the correlative of a vital act, 

 and it ceased when life was extinguished. 



Liidersdorf was the first to show by this method 

 that yeast acted, not, as Liebig had assumed, in virtue 

 of its organic^ but in virtue of its organized character. 

 He destroyed the cells of yeast by rubbing them on a 

 ground glass plate, and found that with the destruction 

 of the organism, though its chemical constituents re- 

 mained, the power to act as a ferment totally dis- 

 appeared. 



One word more in reference to Liebig may find a 

 place here. To the philosophic chemist thoughtfully 

 pondering these phenomena, familiar with the concep- 

 tion of molecular motion, and the changes produced 

 by the interactions of purely chemical forces, nothing 

 could be more natural than to see in the process of 

 fermentation a simple illustration of molecular insta- 

 bility, the ferment propagating to surrounding molecular 

 groups the overthrow of its own tottering combinations. 

 Broadly considered, indeed, there is a certain amount 

 of truth in this theory ; but Liebig, who propounded 

 it, missed the very kernel of the phenomena when he 

 overlooked, or contemned, the part played in fermenta- 

 tion by microscopic life. He looked at the matter too 

 little with the eye of the body, and too much with the 

 spiritual eye. He practically neglected the microscope, 

 and was unmoved by the knowledge which its revelations 

 would have poured in upon his mind. His hypothesis, 

 as I have said, was natural — nay, it was a striking 

 illustration of Liebig's power to penetrate and unveil 



