62 MICRO-ORGANISMS AND FERMENTATION. 



whilst, on the addition of this substance, the lactic acid 

 was proportionately increased. 



In breweries the lactic acid fermentation takes place even 

 in the malting, also in the wort and in the after-fermentation ; 

 in the Belgian beers, obtained by spontaneous fermentation, 

 lactic acid is formed in large quantity, and cousequently 

 imparts a sharp taste to the beer. In modern low-fermenta- 

 tion breweries it is endeavoured to exclude the lactic acid 

 ferment, and bacteria in general, from the fermentations. 

 " In distilleries," according to Maercker, " these are still 

 provisionally regarded as a necessary evil. The production 

 of lactic acid takes place during the yeast-dressing, and its 

 importance appears to be confined to preventing the develop- 

 ment of bacteria, and in this way rendering possible the pure 

 fermentation of the alcoholic yeast." 



FIG. 12. 



Lactic acid bacteria, after Pasteur. In order to give an idea of the size of 

 the bacteria, some yeast-cells are figured amongst them. 



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 his " Etudes sur la biere " he figures some bacteria which 

 develop in wort or beer in which lactic fermentation has set 

 in (Fig. 12) ; he describes them as short rods slightly narrowed 

 in the middle, and commonly occurring singly, rarely united 

 in chains. 



Later, 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 carbonic acid. 

 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 



