WORK OF PASTEUR 93 



that fermentation was due to something borne in by the air, and 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 transforma- 

 tion of sugar into alcohol and carbonic acid gas simply and solely as 

 a non-vital chemical process, depending upon the dead yeast com- 

 municating its own decomposition to surrounding elements 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 

 th"e aid of hving organisms, or any initiative force greater than 

 dead yeast cells. It was at this juncture that Pasteur intervened to 

 dispel the obscurities and contradictory theories which had been 

 propounded. 



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

 ing 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, it begins after a time 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 httle disappears. Pasteur demonstrated the cause of this trans- 

 formation of sugar into lactic acid to be a thin layer of organic 

 matter consisting of extremely 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 fermentation. One series of experiments was 

 accomplished with yeast cells and these bacteria, a second series with 

 living yeast cells only, a third series with bacteria only, and the con- 

 clusions at which Pasteur arrived as the result of these labours he 

 expressed in the following words : — 



" As for the interpretation of the group of new facts which I have 

 met with in the course of these researches, I am confident that who- 

 ever shall judge them with impartiality will recognise that the 

 alcoholic fermentation is an act correlated to the life and to the 

 organisation of these corpuscles, and not to their death or their putre- 

 faction, any more than it will appear as a case of contact action in- 

 which the transformation of the sugar is accomplished in the 

 presence of the ferment without the latter giving or taking anything 

 from it." 



