BACILLUS ACIDI LACTICI. 365 



length of these rods is, according to Hueppe, 1 to 1'7 ^., 

 their breadth *3 to "4 /*., but rods as long as 2*8 p. also 

 occur. The bacilli have no spontaneous movement. In 

 solutions of sugar they show distinct spores, which are 

 also formed in milk, but are much more difficult to 

 recognise in that medium. The spores appear as 

 refracting globules at the ends of ^ 



the bacilli ; if two bacilli are united ***'{ : r ^ 

 together the spores often appear at Fig. 97. Lactic acid 

 the ends furthest removed from bacillus x 700. 



i . . ' , , . . Cover glass preparation 



each other, but often also at the from a fresh cultiva- 

 adjacent ends. Bacilli containing tlon * 

 these spores are not killed when boiled for a short time. 

 The bacilli grow readily on various soils. In gelatine Cultivations. 

 plates they form on the second day whitish colonies, 

 which under a low power, and so long as they are deeply 

 situated, present the form of circular discs, uniformly 

 dark, and with sharp black outlines ; those which occur 

 on the surface are surrounded by a somewhat clearer 

 marginal zone. In puncture cultivations a deposit, 

 which is at first delicate, and later somewhat denser, and 

 which forms at parts discrete spheres, appears along the 

 whole track of the needle. In stroke cultivations the in- 

 dividual colonies, which are at first circular, run together 

 and form a narrow white stripe, with irregular borders. 



Lactic acid fermentation can be set up with pure cul- Conditions cf 

 tivations of these bacilli in solutions of milk sugar, cane fermentation, 

 sugar, mannite, and dextrose. In addition to lactic 

 acid, carbonic acid is also always formed. When more 

 than *8 per cent, of lactic acid is present in the ferment- 

 ing mixture, the progress of the fermentation is inter- 

 fered with, and hence when it is desired to carry the 

 fermentation further it is necessary to add chalk in order 

 to neutralise the acid. 



According to Hueppe, free oxygen is necessary for the Necessity for 

 occurrence of the fermentation ; nevertheless, very xyg( 

 small quantities are sufficient in order to permit the 

 formation of the amount of lactic acid necessary to 

 cause coagulation of the casein ; but larger quantities of 

 acids appear to be formed only when there is a corre- 



