ALCOHOLIC FERMENTS. 119 



fermentation in a sugar solution when no other nourishment 

 is present, and consequently the yeast does not multiply, or 

 does so only to a small extent. Ndgeli therefore states 

 (p. 26) that " Pasteur's theory, that fermentation is induced 

 through want of oxygen, in that the yeast cells are forced 

 to take the necessary supply of oxygen from the fermentable 

 substance, is refuted by all the facts which bear upon this 

 question." 



A. J. Brown, who also holds this view, made a series of 

 experiments in which fermentations were conducted in pre- 

 sence of an abundant supply of oxygen, whilst in a duplicate 

 set - of experiments conducted simultaneously, oxygen was 

 excluded ; the same number of non-multiplying yeast cells 

 were present in both cases, and all the other conditions 

 were kept constant. These experiments showed contrary 

 to Pasteur's theory that the yeast cells exercised a greater 

 fermentative power in the presence of oxygen than when the 

 latter was excluded. 



Recently Hiieppe and his pupils have also opposed 

 Pasteur's theory, and have brought forward examples of 

 fermentation organisms "which can induce the specific 

 fermentations mostly even more readily when atmospheric 

 oxygen is present." 



Of Nageli's manifold work on the lower organisms, we 

 will only mention, as connected with the foregoing, the 

 " molecular-physical " theory of fermentation put forward by 

 him, and which is essentially a modification of Liebig's 

 theory. Whilst Pasteur explains fermentation as the result 

 of activity occurring within the cell, Ndgeli defines fermen- 

 tation as a transference of the vibrations of the molecules, 

 groups of atoms and atoms of different compounds (which 

 themselves suffer no change), contained in the living plasma 

 to the fermentable substance, whereby the equilibrium of its 

 molecules becomes disturbed and their decomposition brought 

 about. In the process of fermentation, the vibrations of the 

 plasma molecules are thus transferred to the fermentable 



