Proceedings. 237 



/Compounds of the plasma or cell-contents to the fermen- 

 table material, without itself being affected," has caused 

 Liebig's chemico- physiological theory, that the cause of 

 fermentation is the communication of internal molecular 

 motion of matter in the course of decomposition to other 

 matter, the elements of which have a feeble affinity, to re- 

 gain some significance. Schlitzenberger repeated Pasteur's 

 experiments, but has given a different explanation. He 

 argues that if the decomposition of sugar were the result of 

 a respiration of the cells of yeast at the expense of com- 

 bined oxygen recruiting the free oxygen, it seems evident 

 that fermentation ought not to take place, or at least ought 

 to be sensibly lessened, in the presence of free oxygen ; but 

 the reverse of this is the case. The respiratory power of yeast 

 is independent of the quantity of oxygen contained in the 

 medium in which it lives ; it only varies with the tempera- 

 ture, and the more or less favourable conditions of nutrition, 

 as well as with the more or less perfect state of health of 

 the cell. The respiratory power and the fermenting power 

 are two qualities inherent in the cell of the SaccJiaroviyces 

 which are not the two variable terms of a constant sum, of 

 which the one vanishes when the other attains its maximum 

 value ; on the contrary, all facts tend to prove that these 

 two values grow weak, are destroyed, or attain their maxima 

 at the same time, under the influence of the same causes. 

 Pasteur and other zymologists have set down the following 

 laws: — (i) The spores of the Ascomycetes, when submerged 

 in a fermentable liquid, require a certain amount of free 

 oxygen in order to bud or develop into yeast ; when once 

 thus developed, they can abstract the requisite oxygen from 

 the compounds contained in the fluid, thereby fermenting 

 the same. Actual fermentation begins the moment the 

 ascospores have developed into yeast cells. (2) On the 

 total absence of free oxygen, the fermentative action of 

 budding yeast may continue for a number of generations, 



