THEORY OF FERMENTATION 375 



bon. Liebig carefully abstained from noticing this fact, 

 which would have been fatal to the very groundwork of his 

 criticisms, and thought that he was keeping up the appear- 

 ance of a grave contradiction by arguing that we had never 

 obtained a simple alcoholic fermentation. It would be un- 

 profitable to dwell longer upon the subject of the difficulties 

 which the propagation of yeast in a saccharine mineral 

 medium formerly presented. As a matter of fact, the progress 

 of our studies has imparted to the question an aspect very 

 different from that which it formerly wore; it was this cir- 

 cumstance which emboldened us to offer, in our reply to 

 Liebig before the Academy of Sciences in 1871, to prepare, 

 in a saccharine mineral medium, in the presence of a com- 

 mission to be appointed by our opponent, any quantity of fer- 

 ment that he might require, and to effect the fermentation of 

 any weight of sugar whatsoever. 



Our knowledge of the facts detailed in the preceding chap- 

 ter concerning pure ferments, and their manipulation in the 

 presence of pure air, enables us completely to disregard those 

 causes of embarrassment that result from the fortuitous 

 occurrence of the germs of organisms different in character 

 from the ferments introduced by the air or from the sides 

 of vessels, or even by the ferment itself. 



Let us once more take one of our double-necked flasks, 

 which we will suppose is capable of containing three or four 

 litres (six to eight pints). 



Let us put into it the following: 



Pure distilled water. 



Sugar candy 200 grammes 



Bi tart rate of potassium i.o " 



" ammonia 0.5 " 



Sulphate af ammonia 1.5 " 



Ash of yeast 1.5 " 



(i gramme = 15.43 grains) 



Let us boil the mixture, to destroy all germs of organisms 

 that may exist in the air or liquid or on the sides of the 

 flask, and then permit it to cool, after having placed, by way 

 of extra precaution, a small quantity of asbestos in the end 

 of the fine curved tube. Let us next introduce a trace of fer- 

 ment into the liquid, through the other neck, which, as we 



