626 VITAL ACTIONS OP THE LOWER FUNGI. 



demonstrated that a part of the sugar from a saccharine 

 Solution in which yeast kept without oxygen is sown, 

 passes into the yeast cells and is there rapidly broken up ; 

 hut this only takes place with regard to a small fraction 

 of the sugar, and it does not occur in every yeast capable 

 of setting up fermentation. Hence the question as 

 regards the seat of the decomposition cannot as yet be 

 decided with certainty ; the great quantity of the material 

 broken up in a short space of time leads at any rate to- 

 the presumption that in fermentation a chemical combi- 

 nation between the protoplasm and fermentescible mate- 

 rials does not occur, but that that process is limited to the 

 ordinary nutritive and respiratory processes of the cells. 

 Nageli's Nageli has in fact put forward some very definite reasons 

 fermentation. f r believing that fermentescible molecules lying outside 

 the cells (but it is true in their immediate neighbour- 

 hood) can be broken up by the movements in the proto- 

 plasm. This is shown, for example, in the formation of 

 acetic ether, which frequently accompanies the alcoholic 

 fermentation; acetic ether is not formed when acetic 

 acid is present in the fermenting mixture ; acetic acid 

 and alcohol must, on the contrary, meet in the nascent 

 state; if both were produced by the same organisms it 

 would be conceivable that they arose and combined 

 within the cells; but the alcohol is formed by yeast cells, 

 the acetic acid by bacteria, and thus their combination is 

 only possible if both the components arise outside the 

 cells. Nageli also observed that bacteria were able to 

 reduce and decolourise litmus colouring-matter, although 

 it could be shown that the colouring material could not 

 penetrate into the living plasma of the cells. Further, 

 numerous observations indicate that the alcoholic- 

 fermentation which occurs in the interior of uninjured 

 fruits is brought about by yeast cells, which have their 

 seat on the skin ; lastly, Nageli explains the fact that in 

 a sugar solution containing large numbers of yeast cells 

 bacteria which may have been present gradually die, by 

 supposing that the movements which are communicated 

 from the plasma of the yeast cells to the sugar molecule 

 ultimately pass on to the bacteria and thus weaken these 



