186 BACTERIOLOGY 



provided with abundant flagella, and which do not liquefy 

 gelatine. Upon the plate there form superficial round 

 colonies, which cause a dark coloration of the surrounding 

 gelatine. Thrust-cultivations grow in the form of the nail- 

 culture, the head of which consists of a thick white deposit. 

 The gelatine is stained greyish-blue, and finally assumes 

 a dark tint. On agar a superficial coat forms, and the 

 medium becomes discoloured. On potatoes there occurs 

 at first a thick, yellow, dirty layer round the inoculated 

 spot, and in older cultures a blue coloration of the medium. 

 The bacillus multiplies by formation of spores occupying 

 a terminal position. The blue pigment is changed to a 

 brilliant red by alkalies, but is restored by the action of 

 acids. According to Gessard, the substance from which it 

 is derived is lactic acid. 



Bacterium lactis erythrogenes. Hueppe and Grotenfeldt 

 found this microbe in red milk, and also in the faeces of 

 children. It consists of short, oscillating rods, the growth 

 of which liquefies gelatine. The colonies are of a yellow 

 colour when first seen on the plate, but after liquefaction 

 they become rose-red. On thrust-cultures there appears a 

 whitish, or later, yellowish layer, which finally acquires the 

 rose-red tint ; when liquefaction has taken place in ten or 

 twelve days the fluid is rose-coloured, and the coloration 

 extends also into the substance of the remaining solid 

 gelatine. A yellowish deposit occurs on agar, and soon 

 changes to yellowish-redr On the surface of potato a golden- 

 yellow colour appears in six to eight days at incubating 

 temperature, whereas at ordinary room temperature the 

 colonies are yellowish-red. All cultures exhale an un- 

 pleasant sweet smell. 



If a small quantity of pure culture be added to neutral 

 or feebly alkaline milk, the caseine is separated out and 

 peptonised, the layer of cream on the surface and the 



