Cultivation 425 



irregular borders (Fig. 127). The growth in gelatin puncture 

 is characterized by the occurrence of small spheric colonies 

 along the line of inoculation. The gelatin is not liquefied. 



Agar-agar. Upon agar-agar and glycerin agar-agar the 

 colonies are slower to develop, larger, more translucent, 

 without the yellowish-white or china-white color of the 

 blood-serum cultures, and are more or less distinctly divided 

 into a small elevated center and a flat surrounding zone 

 with indented edges, and a radiated appearance. When 

 transplantations are made from blood-serum to agar-agar, 

 the resulting growth is usually meager, but the oftener the 

 organism is transplanted to fresh agar-agar, the more luxu- 

 riant its growth becomes. 



Bouillon. When planted in bouillon a distinct, whitish, 

 granular pellicle forms upon the surface of the medium, 

 especially when the culture is freely exposed to the air or 

 made by the method of Fernbach with a passing current of 

 air. This pellicle appears quite uniform when the flask is 



Fig. 127 Bacillus diphtherias ; colony twenty-four hours old, upon agar- 

 agar. X 100 (Frankel and Pfeiffer). 



undisturbed, but is so brittle that it at once falls to pieces if 

 the flask be moved, the minute fragments slowly sedimenting 

 and forming a miniature snow-storm in the flask or tube. 

 The organism at times also causes a diffuse cloudiness of the 

 medium, but, not being motile, soon settles to the bottom 



