428 PLAGUE 



spores. Gordon, who has found that they possess 

 which, however, stain with difficulty, states that they are 

 motile. Most observers, however, and with these we agree, 

 have failed to find evidence of true motility. They stain readily 

 with the basic aniline stains, but are decolorised by Gram's 

 method. 



Cultivation. From the affected glands, etc., the bacillus can 

 readily be cultivated on the ordinary media. It grows best at 

 the temperature of the body, though growth occurs as low as 

 18 C. On agar and on blood serum the colonies are whitish 



circular discs of somewhat 

 transparent appearance 

 and smooth, shining sur- 

 face. When examined 

 with a lens, their borders 

 appear slightly wavy. In 

 stroke cultures on agar 

 there forms a continuous 

 line of growth with the 

 same appearance, showing 

 partly separated colonies 

 , at its margins. When 



agar cultures are kept at 

 the room temperature, 

 some of the colonies may 

 show a more luxuriant 



growth with more opaque 

 FIG. 146. Culture of the bacillus of plague & 



on 4 per cent salt agar, showing involution appearance than the rest 



forms of great variety of size and shape. of the growth, the appear- 



Stained with carbol-thionin-blue. x 1000. ance in fact being often 



such as to suggest the 



presence of impurities in the cultures. In stab cultures in 

 peptone gelatin, growth takes place along the needle track as 

 a white line, composed of small spherical colonies. On the 

 surface of the gelatin a thin, semi-transparent layer may be 

 formed, which is usually restricted to the region of puncture, 

 though sometimes it may spread to the wall of the tube ; some- 

 times, however, there is practically no surface growth. There is 

 no liquefaction of the medium. In gelatin plates the superficial 

 colonies develop first and form slightly raised semi-transparent 

 discs with somewhat crenated margins ; the deeper colonies are 

 smaller and of spherical shape with smooth outline. In bouillon 

 the growth usually forms a slightly granular or powdery deposit 

 at the foot and sides of the flask, somewhat resembling that of 



