ORIGIN OF THE YEASTS OF WINE 



217 



But let us leave this dust, evidently living, in a thin 

 layer of sugar solution exposed to the air under the micro- 

 scope, and we shall see come forth in profusion from 

 certain groups of the brown corpuscles, cells (Ai, Ao, 

 Bi, Bo, Fig. 19) or branching filaments which at once 

 bud and segment into cells. Now these cells are yeast 

 cells, for, once rejuvenated in contact with air and sown 

 in a sweet must, they produce in some hours an active 

 alcoholic fermentation. 



Pasteur must have felt a profound joj^ in discovering 



# 



O 



B 



Fig. 19. Thick-walled brown cells that give rise to wine yeasts. 



these facts, for, with his usual perspicacity, he must 

 have seen immediately the solution of a problem which 

 had been in his mind for a long time, and of which 

 he had many times tried in vain to find the solution. 

 The origin of this difficulty was the experiment of Gay- 

 Lussac which we have described, and in which this scien- 

 tist had seen some bubbles of oxygen produce fermen- 

 tation in the juice of grapes crushed in a test-tube under 

 mercury and remaining inert up to that time. 



It is here that we can find a proof of the truth of that 



