112 BACTERIA 



that this something was yeast. Passing over a number of 

 counter-experiments of Helmholtz and others, we come to 

 the work of Liebig. ( He viewed the transformation of sugar 

 into alcohol and carbonic acid gas simply and solely as a 

 non-vital chemical process, depending upon the dead yeast 

 communicating its own decomposition to surrounding ele- 

 ments in contact with it. ) 



Liebig insisted that all albuminoid bodies were unstable, 

 and if left to themselves would fall to pieces i. e., ferment 

 without the aid of living organisms, or any initiative force 

 greater than dead yeast cells. It was at this juncture that 

 Pasteur intervened to dispel the obscurities and contradic- 

 tory theories which had been propounded. 



As in all the conclusions arrived at by Pasteur, so in those 

 relating to fermentation, there were a number of different 

 experiments which were performed by him to elucidate the 

 same point. We will choose one of many in relation to 

 fermentation. If a sugary solution of carbonate of lime is 

 left to itself, after a time it begins to effervesce, carbonic 

 acid is evolved, and lactic acid is formed ; and this latter 

 decomposes the carbonate of lime to form lactate of lime. 

 This lactic acid is formed, so to speak, at the expense of 

 the sugar, which little by little disappears. Pasteur demon- 

 strated the cause of this transformation of sugar into lactic 

 acid to be a thin layer of organic matter consisting of ex- 

 tremely small moving organisms. If these be withheld or 

 destroyed in the fermenting fluid, fermentation will cease. 

 If a trace of this grey material be introduced into sterile 

 milk or sterile solution of sugar, the same process is set up, 

 and lactic acid fermentation occurs. 



Pasteur examined the elements of this organic layer by 

 aid of the microscope, and found it to consist of small short 

 rods of protoplasm quite distinct from the yeast cells which 

 previous investigators had detected in alcoholic fermenta- 

 tion. One series of experiments was accomplished with 



