ALCOHOLIC FERMENTS. 137 



results is incongruous with the opposite view of the nature of 

 fermentation, namely, that the yeast-cell exercises its functions 

 independently of its surroundings, e.g. of the presence or 

 absence of free oxygen. 



HUEPPE and his pupils have also opposed PASTEUR'S theory, 

 and have brought forward examples of fermentation organisms 

 " which can induce the specific fermentations even more readily 

 when atmospheric oxygen is present." 



Of NAEGELI'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, which is 

 essentially a modification of LIEBIG'S theory. Whilst PASTEUR 

 explains fermentation as the result of activity occurring within 

 the cell, NAEGELI defines fermentation 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 substance. The active cause of 

 fermentation is present in the living plasma, and therefore in 

 the interior of the cells ; but it operates at a moderate distance 

 outside the cell. The decomposition of sugar into alcohol and 

 carbonic acid takes place to a small extent within, but mainly 

 outside the yeast-cells. This theory is thus distinctly opposed to 

 that of PASTEUR, and follows on the lines of the theories 

 propounded by STAHL and LIEBIG. 



IWANOWSKY, on the basis of experiments made with abso- 

 lutely pure cultures, holds the opinion that the supply of 

 oxygen during fermentation exerts no influence on the fer- 

 mentative power of yeast ; he found that the same quantity of 

 yeast fermented the same amount of sugar, whether the 

 fermenting liquor was agitated by means of a strong blast 

 of air or whether the fermentation took place in pure nitrogen; 

 according to this observer the alcoholic fermentation performed 

 by the yeast-cell depends simply on the composition of the 

 nutritive liquid. He looks upon this function as the result 

 of a diseased state which has been brought about during 



