LACTIC ACID BACTERIA. 109 



In 1884, Hueppe found a bacterium in a spontaneous 

 lactic acid fermentation which converts lactose and other 

 sugars into lactic acid with the simultaneous formation of 

 carbon dioxide (Bacillus acidi lactici). It consists of short, 

 plump, motionless cells, the length of which exceeds their 

 breadth by at least one-half ; they are united chiefly in pairs, 

 and seldom in groups of four. In gelatine plates they form 

 whitish colonies ; those below the surface are stellate, uni- 

 formly dark, and sharply outlined ; on the surface they appear 

 as flat white glistening nodules, resembling porcelain surrounded 

 by clear outer zones. Atmospheric oxygen is necessary for 

 fermentation with this species. 



In recent times a large number of species of lactic acid 

 bacteria have been found in milk. Marpmann, in 1886, 

 described five species embracing both coccus and longer and 

 shorter rod forms, and showed that the whole series was 

 capable of producing a slight formation of alcohol. 



. 



O 



Fig. - 22. Lactic acid bacteria (after Pasteur). In order to give an idea of the size of the 

 bacteria, some yeast cells are figured among them. 



Hueppe and Grotenfelt have since described new species, 

 of which Grotenfelt 's Streptococcus acidi lactici appears to be 

 identical with the Bad. lactis acidi described by Leichmann. 



Adametz and Freudenreich have isolated species from 

 Emmenthaler cheese (Bac. casei) which are for the most part 

 facultative anaerobes. 



Leichmann has thrown new light on the conditions present 

 during the spontaneous souring of milk. He found that a 

 single species or type strongly preponderated, and named it 

 Bact. lactis acidi (Streptococcus lacticus}. He described it as 

 consisting of short motionless rods about one and a half times 

 as long as they are broad, sometimes present in pairs, sometimes 

 in chains (the latter particularly when cultivated in sugar- 

 broth). On gelatine plates, the immersed colonies consist of 

 round discs, white or pale yellowish-brown, at first transparent, 



