208 STUDIES ON FERMEN'TATIOIS'. 



mentation completed, we leave the liquid to itself, not touching 

 the flask again. The fermented liquor covers a deposit of 

 yeast, apparently inert, and no trace of mycodenna vini makes 

 its appearance on the surface of the liquid. Let us suppose 

 that we gc on daily for a considerable time introducing a little 

 of the yeast from this flask to a difiierent flask of wort : the 

 fresh flasks will begin to ferment. The only appreciable dif- 

 ference which these successive flasks will present, their impreg- 

 nation having been effected at intervals of twenty-four hours, 

 will be that, ceteris joanbus, fermentation in them will be more 

 and more slow in making its appearance. This difterence, as 

 we have already explained, will be due to the fact that the 

 yeast in the first flask will, in the course of time, undergo, 

 in each of its cells, a process which we cannot better describe 

 than as a progressive senescence. The cells gradually become 

 filled with amorphous granulations, their interior becomes 

 yellow, and the protoplasm collects, either at the centre or 

 near the borders ; in short, the vitality of the yeast becomes 

 feeble. When, however, it is taken out of the liquid in which 

 it has fermented and introduced into a fresh saccharine wort, 

 it gradually resumes its transparency, and then begins to 

 germinate. These effects are the less rapidly brought about 

 the longer the cells remain exhausting themselves in the first 

 fermented liquid. They might be left in that liquid for such 

 a length of time that they would eventually perish, a fact 

 which would manifest itself in their absolute sterility and 

 quiescence when sown in a fresh medium. In general, however, 

 matters are not carried far enough for this to take place, and 

 the yeast, preserved in a state of purit}^ in its fermented 

 liquid, retains the capacity of revival, which ma}- then go on 

 indefinitely. As a matter of observation, the cells of yeast, 

 after causing the liquid to ferment, instead of remaining 

 inactive, and so by living at their own expense gradually 

 passing into a state of exhaustion, begin to bud again ; at least 

 this is true of many of them. Multiplying afresh in the 

 fermented medium, under the influence of the air, they form 



