LACTIC ACID FERMENTATION 155 



organisms, a Torula and a Penicillium, which latter he thought 

 was the cause of lactic fermentation. 



Rowlandson, under the influence of Liebig, defined the pre- 

 liminary conversion of lactose into lactic acid in the souring of 

 milk as an oxidation process, and expressed the opinion that a 

 cow that had been in active exercise (and therefore breathing 

 rapidly before milking) would yield a milk rich in oxygen, and 

 therefore liable to turn sour with unusual rapidity. 



Pasteur, as we have already pointed out, was the first to describe 

 an organism characteristic of lactic fermentation, and to prove 

 that it was capable of producing acidification in a sweet, sterile 

 milk. This organism, which Pasteur named the "ferment, or 

 yeast, of lactic fermentation " {leviire lactique) was a bacterium. 

 Pasteur demonstrated the difference existing between this "fer- 

 ment" and that of alcoholic fermentation, by proving that in 

 media containing sugar, the former organism always set up lactic 

 acid fermentation, whilst the latter invariably gave rise to alcoholic 

 fermentation. Pasteur noticed that in cases of apparently spon- 

 taneous souring of milk there was a greyish deposit, and that the 

 quantity of this increased as the process advanced. By microscopic 

 examination this deposit was found to consist of rod-like corpuscles 

 possessing marked differences from the alcoholic ferment. Pasteur 

 then introduced a trace of this deposit into a solution of sugar to 

 which he had added a decoction of yeast and some chalk, and in 

 this artificially prepared liquid he thus obtained lactic acid fer- 

 mentation. From this fermenting fluid he again transferred a 

 slight trace to a similar solution of sugar, and so on, invariably 

 obtaining the lactic fermentation and invariably finding the same 

 corpuscles in the deposit Such characteristics as these were more 

 fundamental than were morphological differences, and justified 

 Pasteur in concluding that in this deposit he had found the 

 specific agent of lactic fermentation.^ 



In 1877 Lister was able, by means of the "dilution method," to 

 isolate from sour milk, in a form of pure culture, an organism to 

 which he gave the name B. lactis^ and which he believed gained 

 access to milk from the air of dairies and similar places.- For 

 some time this organism was held to be causally related to 

 lactic fermentation. But in 1884, by means of culture on solid 

 media, as introduced by Koch, Hueppe was able to isolate a 



' In his Etudes sur la Biere, Pasteur describes organisms found by him 

 growing in wort or beer in which lactic fermentation was proceeding. 

 2 Trans, of Path. Soc., 1878, p. 437. 



