294 



LOUIS PASTEUR 





was the maximum amount of oxygen, supposing the greatest 

 possible quantity to have been absorbed, that was required 

 by the yeast formed in the fermentation of 150 grammes 

 (4.8 Troy ounces) of sugar. We shall better understand the 

 significance of this result later on. Let us repeat the fore- 



Fic. a 



going experiment, but under altered conditions. Let us fill, 

 as before, our flask with sweetened yeast-water, but let this 

 first be boiled, so as to expel all the air it contains. To 

 effect this we arrange our apparatus as represented in the 

 accompanying sketch. (Fie. 2.) We place our flask, A, on 

 a tripod above a gas flame, and in place of the vessel of 

 mercury substitute a porcelain dish, under which we can put 

 a gas flame, and which contains some fermentable, sac- 

 charine liquid, similar to that with which the flask is filled. 

 We boil the liquid in the flask and that in the basin simul- 

 taneously, and then let them cool down together, so that as 

 the liquid in the flask cools some of the liquid is sucked from 

 the basin into the flask. From a trial experiment which we 



I 



