364 BACILLI WHICH CAUSE FERMENTATION. 



result, the casein coagulates, was first ascribed by Pasteur 

 to the action of definite micro-organisms. Nevertheless, 

 Lister seems to have been the first to obtain a pure 

 cultivation of lactic acid bacteria by the employment of 

 Formation of the so-called dilution method. As the result of the 



lactic acid by ..... f . 



various kinds investigations oi the last tew years the views advocated 



>f bacteria, ^y Pasteur and Lister have in so far undergone an 

 important modification in that, according to more recent 

 experience, the power of forming lactic acid from carbo- 

 hydrates, and more especially from the milk sugar of the 

 milk, evidently appertains to a large number of species of 

 bacteria, and differences among these species exist mainly 

 as regards the quantitative production by each kind. 

 For example, this property is possessed by all the 

 pyogenic organisms, more especially by the staphylo- 

 cocci, then by the bacillus oxytocus perniciosus ; the 

 bacterium coli commune, and bacterium lactis aerogenes ; 

 further, by a species of bacteria isolated by Miller from 

 carious teeth ; lastly, according to Hueppe's experience, 

 by bacillus prodigiosus, and by a species of coccus 

 isolated from the secretion of the mouth, and growing 

 in the form of flat white knobs. Undoubtedly the 

 number of organisms which are capable of causing lactic 

 acid fermentation is not exhausted by these 15 species. 



Nevertheless, one definite organism seems to have the 

 right to the designation " lactic acid bacterium," because 

 it is evidently by far most frequently the cause of the 

 spontaneous clotting of milk, and because also it is 

 marked out from the other bacteria which have a similar 

 action by its wide distribution, and by the intensity of 



Lactic acid its effect. This lactic acid bacillus has been accurately 

 described by Hueppe, and is probably identical with 

 that observed by Lister and Pasteur. 



Morphological This bacillus forms short, thick cells, which are at 

 least half as long again as broad, and are usually united 

 in pairs, seldom in fours. Under too low a power the 

 individual cells may present the appearance of oval cocci, 

 but when more highly magnified we see distinctly that 

 the outlines are parallel, and that the ends are slightly 

 narrowed in the longitudinal direction. The average 



