BACTERIA. 69 



their refreshing taste to a vigorous lactic acid fermentation. 

 In modern low-fermentation breweries every endeavour is 

 made to exclude the lactic acid ferment, and bacteria in 

 general, from the fermentations. In distilleries, on the other 

 hand, lactic acid bacteria are cultivated methodically, with 

 the view of either directly suppressing other bacteria, especi- 

 ally butyric acid bacteria, or, at least, bringing about the 

 most unfavourable conditions for their growth. (See below.) 



We are indebted to PASTEUR for the first important work 

 on the subject of lactic acid bacteria. In 1858 he described 

 the species which appears when 

 milk spontaneously ferments. In oo ^J> 



his "Etudes sur la biere " he ^ \<9 a * 



depicts certain bacteria growing /^ <= ^^ O 



in wort or beer in which lactic * oS^l Q" "^* 

 fermentation has begun (Fig. 19); * 



i 1 -i -i i i FIG. 19. Lactic acid bacteria. (After 



lie describes them aS SilOrt rOdS PASTEUR.) In order to give an idea of 



slightly narrowed in the middle, ^S^^^ 7 ***^ 

 and commonly occurring singly, 



rarely united in chains. In 1877 LISTER prepared from sour 

 milk a pure culture of a lactic acid bacterium, which he 

 called bacterium lactis. 



More recently, HUEPPE found a bacterium in a spontaneous 

 lactic acid fermentation which converts milk-sugar 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 in pairs or 

 in groups of four. In sugar solutions and less distinctly 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, with sharp contours and uniformly dark appear- 

 ance ; those on the surface have lighter borders. Atmospheric 

 oxygen is necessary for fermentation with this species. It 

 coagulates the caseine of milk. 



In recent publications descriptions are found of a large 

 number of lactic acid bacteria ; thus, two species of micrococci 

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



