SOURING CREAM. 



117 



tinguished from each other by the fact that some are connected 

 in chains, others are not (Fig. 23) ; the latter are of the most 

 frequent occurrence, and are most widely distributed. These 

 forms bear a certain resemblance to Pasteur's " ferment 

 lactique." The species represented in Fig. 23, B, was isolated 

 by Storch from a sample of butter having a pure and full 

 aroma. It forms small globular colonies in gelatine of a pure 

 white colour and smooth surface. In milk and whey it occurs 

 in oval or globular forms. These lactic acid bacteria display 

 fermentative activity, even at 20 C. At 28 C. milk is turned 

 sour within eight to nine hours. 



Many species have been isolated by Weigmann and intro- 



Fig. 23. Lactic acid bacteria (after Storch). 



duced into practice. A species which has been very success- 

 fully applied at several places was prepared by Quist, and 

 afterwards by J. C. Holm in the author's laboratory. It 

 occurs both as micrococcus and in other forms, according to 

 the different nutrient media in which it is cultivated. On 

 gelatine it forms small, circular, slowly-growing colonies of 

 a * whitish-yellow colour. In stab-cultures spherical colonies 

 arise throughout the puncture-channel, and in streak-cultures 

 this organism forms a continuous streak with wavy borders. 

 It was prepared from a sample of butter of remarkable aroma 

 and durability. 



Pure cultures of lactic acid bacteria have also been applied 



