372 BACTERIOLOGY. 



about this point. In the centre of the depression can 

 be distinguished a small, dense, whitish clump, the col- 

 ony itself. As growth continues the depression increases 

 in extent and ultimately assumes an appearance that 

 consists in the apparent sinking of the liquefied portion 

 in such a way as to leave a perceptible air-space between 

 the top of the liquid and the surface of the solid gelatin. 

 The growth now appears to be capped by a small air- 

 bubble. The impression given by it at this stage is not 

 only that there has been a liquefaction, but also a coin- 

 cident evaporation of the fluid from the liquefied area 

 and a constriction of the superficial opening of the 

 funnel. (See a, 6, c, and c?, Fig. 74.) Liquefaction is 

 not especially active along the deeper portions of the 

 track made by the needle, though in stab-cultures in 

 gelatin the liquefaction is much more extensive than 

 that usually seen around colonies on plates. It spreads 

 laterally at the upper portion, and after about a week a 

 large part of the gelatin in the tube may have become 

 fluid, and the growth will have lost its characteristic 

 appearance. 



Stab- and smear-cultures on agar-agar present noth- 

 ing characteristic. They are usually only an exagger- 

 ation of the appearance afforded by the single colonies 

 on this medium. 



Its growth in bouillon is luxuriant, causing a diffuse 

 clouding and the ultimate production of a delicate film 

 upon the surface. 



In sterilized milk of a neutral or amphoteric reaction 

 at a temperature of 36-38 C. it develops actively, 

 and gradually produces an acid reaction with coagula- 

 tion of the casein. It retains its vitality under these 

 conditions for about three weeks or more. The blue 



