46 LOUIS PASTEUR. 



Pasteur ? For the simple reason that chemists had 

 never observed the production of lactic fermentation 

 except in complex substances. They mixed chalk 

 with their milk for the purpose of presew-jftg^the 

 neutrality of the fermenting medium. They em- 

 ployed substances such as caseine, gluten, animal 

 membranes, all of which, when examined by the 

 microscope, exhibited a multitude of mineral or 

 organic granules, with which the lactic ferment was 

 confounded. Thus the first care of Pasteur, with tfpp 

 view of proving the presence of the ferment and its 

 life, was to replace the cheesy matter and all its 

 congeners by a soluble, nitrogenous body, which would 

 permit of the microscopic examination of all the living 

 cellular products. 



In a memoir presented to the Aqademy of Sciences 

 in 1857 Pasteur stated that there were * cases where 

 it is possible to recognise in lactic fermentation, as 

 practised by chemists and manufacturers, above the 

 deposit of chalk and the nitrogenous matter, a grey 

 substance which forms a zone on the surface of the 

 deposit. Its examination by the microscope hardly 

 permits of its being distinguished from the disinte- 

 grated caseum or gluten which has served to start the 

 fermentation. So that nothing indicates that it is a 

 special kind of matter which had its birth during the 

 fermentation. It is this, nevertheless, which plays the 

 principal part.' 



