GENUS BACILLUS 



345 



o 



they exhibit polar germination. The few flagella are arranged 

 about the organism. 



Staining. It is colored 

 with the ordinary bacterial 

 staining solutions. It is 

 Gram positive. 



Cultivation. It can be 

 cultivated o n ordinary 

 media. It grows at room 

 temperature but better at 

 37 C. 



Agar. A gray layer 

 spreads over the surface in 

 24 hours, which later takes 

 on a slightly brown color. 

 A heavy slightly viscid 

 growth occurs in the con- 

 densation water. On agar 

 plates, small, grayish, cir- 

 cular colonies form in 24 

 hours. When many are on 

 the plate, they do not ex- 

 ceed 2 mm. in diameter. 

 Under low magnification 

 they appear granular, with 

 no definite margin. 



Gelatin. It develops 

 slowly in gelatin. The colo- 

 nies become very irregular in outline, owing to thread-like out- 

 growths which take place in curves from its border. Growth 

 is better when 5% glycerin is added. From the small, white, 

 spherical colonies which form along the line of puncture gray, 

 threadlike growths shoot out through the medium. In about 2 

 months the gelatin is changed to a thick liquid, holding gray 

 flocculent masses of organisms which gradually settle, forming 

 a strong, slightly viscid sediment. 



Potato. On this medium the bacillus grows rather slowly 



Fig. 70. Bacillus alvei. (1) Gela- 

 tin stab culture showing the char- 

 acter of the growth of colonies; (2) 

 beginning of spore formation; (3) 

 later stages in spore formation; and 

 (4) free spores, 2, 3 and 4 much en- 

 larged (White). 



