FERMENTATION. 49 



might still find some credit, Pasteur worked earnestly 

 to discover new facts capable of demonstrating that 

 Liebig's theory was absolutely false. He made two 

 crucial experiments, the one relating to the yeast of 

 beer, or of alcohol, and the other relating to the lactic 

 ferment. He introduced into a pure solution of sugar 

 a small quantity of crystallisable salt of ammonia, 

 then some phosphates of potash and magnesia, and 

 he sowed in this medium an imponderable quantity, 

 if we may so express it, of fresh cells of yeast. The 

 cells thus sown multiplied, and the sugar fermented. 

 In other words, the phosphorus, the potassium, the 

 magnesium of the mineral salts, united to form the 

 substances which compose the ferment. By this ex- 

 periment, so simple and yet so demonstrative, the 

 power of the organisation of the ferment was once 

 for all established. The contact theory of Berzelius 

 had no longer any meaning, since it was evident that 

 the fermentable matter here furnished to the ferment 

 one of its essential elements, namely, carbon. Liebig's 

 theory of communicated molecular motion, originating 

 in a nitrogenous albuminoid substance, had no better 

 claim, since such substances had been discarded. The 

 whole process took place between the sugar and a 

 ferment germ which owed its life and development to 

 nutritive matters, the most important of which was 

 the fermentable substance. Fermentation, in short, 

 was simply a phenomenon of nutrition. The ferment 



