BACTERIA. 63 



in milk they form spores, which appear as lustrous spheres 

 attached to the end of the rods. In gelatine-plates they 

 form whitish colonies which, as long as they are submerged, 

 are circular, uniformly dark, and have sharp contours ; those 

 on the surface have lighter borders. Atmospheric oxygen is 

 necessary for fermentation with this species. It coagulates 

 the casei'ne of milk. 



In recent publications descriptions are found of a large 

 number of lactic acid bacteria ; thus, two species of micro- 

 cocci have been found in saliva and the mucus of teeth ; 

 amongst the pigment-forming bacteria, species are also found 

 which, in addition to their pigment-fermentation, are able to 

 produce so much lactic acid from the sugar of milk that the 

 casei'ne of the milk coagulates ; to these belong, according to 

 Hueppe, the famous blood-portent (Micrococcus prodigiosus) 

 and, according to Krause, a pathogenic form, the micrococcus 

 of osteo-myelitis. 



According to statements made by Delbriick, Zopf has 

 obtained a lactic acid bacterium by preparing a mash from 

 200 grams of dry malt and 1000 grams of water, and 

 keeping it for some time at 50 C. The material was then 

 sown in a solution of milk-sugar, on the surface of which the 

 organism formed a film. The filaments consist at first of 

 small rods, later of both rods and cocci. 



Peters found a bacterium in leaven, which produces a typical 

 lactic acid fermentation. In plate-cultures it forms circular 

 colonies with concentric stratification. The rods have a rapid 

 sinuous motion ; in a neutral solution of sugar in yeast-water 

 at 30 C., this species forms after some time a slimy film ; 

 the rods have here developed into long filaments. Spore- 

 formation has not been observed. 



The so-called Pediococcus acidi lactici examined by 

 Lindner gives, when cultivated in a neutral malt-extract 

 solution at 41 C., a strong acid reaction ; both in a solution 

 of this kind and in a hay-decoction, which have not been 

 sterilised, this bacterium develops so vigorously that, accord- 



