480 BACTERIOLOGY. 



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 fun- 

 nel. (See a, b } c, and d, Fig. 77.) 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. 



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 to 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 

 color of milk to which neutral litmus tincture has been 

 added is changed to phik after thirty-six or forty-eight 

 hours at body-temperature. 



Its growth in peptone solution, either that of Dun- 

 ham (see Special Media) or the one preferred by Koch, 

 viz., 2 parts of Witters peptone, 1 part of sodium chlo^ 

 ride, and 100 parts of distilled water, is accompanied by 



