138 MICRO-ORGANISMS AND FERMENTATION. 



the nutrition of the yeast-fungus, due to the abnormal com- 

 position of the liquid. The normal nutritive liquid contains a 

 small amount of sugar and about twice as much peptone ; in 

 such a liquid the yeast multiplies freely, and feeds like other 

 fungi without exciting any true alcoholic fermentation. On the 

 other hand, he asserts that the so-called " molecular respira- 

 tion"- in which, among other substances, alcohol is produced 

 depends in yeast, as in other plants, on the absence of free 

 oxygen, and that this function manifests itself plainly if yeast 

 is developed in a liquid containing but a small amount of sugar. 



GILTAY and ABERSON, on the contrary, have confirmed the 

 results of PEDERSEN and HANSEN, showing that a given weight 

 of yeast produces more alcohol in non-aerated cultures than in 

 aerated. They presume that the fact of yeast multiplying 

 more freely when air is blown in may depend on the move- 

 ment set up in the culture liquid, and on the consequent 

 improved nutrition of the yeast-cells. 



EMIL FISCHER has, by purely chemical research, resulting in 

 his celebrated work on the synthesis of the sugars, on the use of 

 phenyl-hydrazin, and the osazone-reaction, diverted the current 

 views on fermentation phenomena into new channels. His 

 researches led him to explain the behaviour of the yeast-cell 

 towards the particular sugar of the nutritive liquid in the 

 same way as the action of the enzymes (invertase, emulsin), 

 so that the chemical activity of the living cell does not differ 

 from the action of chemical ferments. According to FISCHER, 

 fermentation of polysaccharides is always preceded by hydrolysis 

 of the sugar. But there exists an exact relation between the 

 molecular structure of a given sugar and the sugar inverting 

 enzyme of a yeast-cell ; if a sugar comes into contact with the 

 albuminoids of a yeast-cell, which play the most important 

 part among the agents of which the living cell makes use, the 

 sugar is decomposed only if its configuration, the geometrical 

 structure of its molecules, does not deviate too much from the 

 configuration of the molecules of the albuminoid. Thus, accord- 

 ing to FISCHER'S theory, the function of the living cell depends 

 much more upon the molecular geometry than on the composi- 

 tion of the nutritive material. 



Another way in which FISCHER, and also THIERFELDER, 



