HERMANN VON HELMHOLTZ 



process. Thus a temperature of from 20 C. to 24 

 C. was most favourable to it, while the process was 

 arrested at 60 C. Boiling destroyed fermentation. 

 It was also arrested by freezing, but on careful thaw- 

 ing the process was resumed. Schwann also estab- 

 lished the identity of the processes of fermentation 

 and putrefaction by showing that they both were 

 connected with the development of living organisms, 

 and he laid the foundation for the splendid researches 

 of Pasteur, which have created the modern science of 

 bacteriology. 



The contribution made to this discussion by Helm- 

 holtz in 1843 is of no mean importance. He showed, 

 first, that the oxygen produced by electrolysis in a 

 sealed-up tube containing boiled fermentable fluid, 

 did not cause fermentation. He also performed the 

 following ingenious experiment : he placed a bladder 

 full of boiled grape juice in a vat of fermenting juice, 

 and found that the fluid in the bladder did not ferment. 

 Thus the cause of the fermentation could not pass 

 through the wall of the bladder. If the fermentation 

 were excited, as held by Liebig, by a substance formed 

 by the yeast cells, and presumably soluble, one would 

 have expected it to pass through the wall of the 

 bladder ; but if the process were caused by the small 

 yeast cells, then one can see why fermentation was 

 not excited, as the yeast cells could not pass through 

 the membrane. Soon afterwards Mitscherlich showed 

 that the yeast cells could not pass through a septum 

 28 



