Cultivation 367 



sues, by the plate method, or by the inoculation into animals and 

 recovery of the micro-organisms from their blood. 



Cultivation. — Colonies. — Upon the surface of a gelatin plate the 

 bacillus forms beautiful and highly characteristic colonies. To the 

 naked eye they appear first as minute round, grayish-white dots. 

 Under the microscope they are egg-shaped, shghtly brown and granu- 

 lar. Upon the surface of the medium, they spread out into flat, 

 irregular, transparent tufts like curled wool, and from a tangled cen- 

 ter large numbers of curls, made up of parallel threads of bacilli, 

 extend upon the gelatin. Before the colony attains to any consider- 

 able size liquefaction sets in. Beautiful adhesion preparations can 



Fig. 126. — Bacillus anthracis; colony upon a gelatin plate. X loo (Frankel 



and Pfeiffer). 



be made if a perfectly clean cover-glass be passed once through a 

 flame and laid carefully upon the gelatin, the colonies being picked 

 up entire as the glass is carefully removed. Such a specimen can 

 be dried, fixed, and stained in the same manner as an ordinary cover- 

 glass preparation. 



Gelatin Punctures.- — In gelatin puncture cultures the growth is 

 even more characteristic than are the colonies. The bacilli begin to 

 grow along the entire track of the wire, but develop most luxuriantly 

 at the surface, where oxygen is plentiful and where a distinct shaggy 

 pellicle is formed. From the deeper growth, fine filaments extend 

 from the puncture into the surrounding gelatin, with a beautiful 

 arborescent effect. 



Liquefaction progresses from above downward until ultimately 

 the entire gelatin is fluid and the growth sediments. 



Agar-agar. — Upon agar-agar characteristic appearances are few. 

 The growth takes place along the hne of inoculation, forming a 



