APPEARANCES OF CULTURES 



371 



(Fig. 114). These appearances,;, which are well seen on the 

 third or fourth day, resemble those seen in agar plates, as already 

 described in the method of isolation ; but on gelatin the surface 

 colonies are rather more transparent than those on agar. Their 

 characters, as seen under a low power of the microscope, also 

 correspond. If a gelatin tube be inoculated and incubated at 

 37 C., a uniform turbidity- is produced (cf. b. coli, p. 362). 



A. Stab culture of the typhoid Bacillus in gelatin, five days' growth. 



B. Stroke culture of the typhoid bacillus on gelatin, six days' growth. 



C. Stab culture of the bacillus coli in gelatin, nine days' growth ; the gelatin 



is split in its lower part owing to the formation of gas. 



In stroke cultures on agar there is a bluish-grey film of 

 growth, with fairly regular margins, but without any character- 

 istic features. This film is loosely attached to the surface, and 

 can be easily scraped off. 



The growth on potatoes is important. For several days (at 

 incubation temperature) after inoculation there is apparently na 

 growth. If looked at obliquely, the surface appears wet, and if 

 it is scraped with the platinum loop, a glistening track is left : a 



