216 SPECIAL BACTERIOLOGY 



BACILLUS ACIDI LACTICI (HUEPPE). 



Found in sour milk. This organism is without doubt identical 

 with the Bacterium lactis discovered by Lister in 1877. Lister also 

 discovered that lactic acid bacteria, although frequently found in 

 dairies, are very seldom found in the open air. 



Microscopical Appearances. Non-motile rods 1-0 to 1-7 /x long, 

 and 0'3 to 0'4 /x broad, mostly in pairs, but sometimes arranged in 

 small chains. 



Spore Formation absent. 



Biological Characters. Facultative anaerobe ; optimum tempera- 

 ture, 37 C. 



On Gelatine Plates. Flat diffuse superficial colonies with irregular 

 borders, resembling those of Bacterium coli commune. 



In Gelatine Stab Cultures. A nail-shaped growth. 



On Agar. A yellowish-white coating. 



On Potatoes. A yellowish-brown coating. 



In Milk, it forms an acid which precipitates the casein, producing 

 alcohol and CO 2 . 



The above organism is not the only organism that changes milk- 

 sugar into lactic acid, but it is probably the common cause of the 

 spontaneous souring of milk. 



BACILLUS LACTIS ACIDI (LEICHMANN). 



This bacillus was found by Leichmann in milk, which, when 

 maintained at 50 C., underwent spontaneous lactic acid fermentation. 

 When cultivated in sterile milk it forms lactic acid, which turns 

 polarized light to the left. 



BACILLUS LACTICUS (GUNTHER AND THIERFELDER). 



Found in sour milk. 



Non-motile bacilli, 0*5 to 0*6 by I/O /x, usually arranged in pairs 

 or small chains. It does not produce spores, but stains by the Gram 

 method. 



Biological Characters. Grows best at 28 C., and better on media 

 containing sugar than on the ordinary media. 



Gelatine Media are not liquefied. The developing colonies remain 

 very small, but well marked. 



On Potatoes the development is very scanty. 



In Bouillon. A turbid growth which does not cause any change in 

 the reaction. 



