490 



PLAGUE 



of considerable length are present. After a time involution 



forms appear, especially 

 when the surface of the 

 agar is dry ; but the forma- 

 tion of these is much more 

 rapid and more marked 

 when 2 to 5 per cent, of 

 sodium chloride is added to 

 the medium, constituting 

 the so-called "salt agar" 

 (Hankin and Leumann). 

 On this medium, especially 

 with the higher percent- 

 age, the involution forms 

 assume a great size and a 

 striking variety of shapes, 



FIG. U6.-Bacillus of plague from a young ^ g lo k ular > oval > r 

 culture on agar. pyriform bodies resulting 



Stained with weak carbol-fuchsin. x 1000. (Fig. 148); with about 2 



per cent, sodium chloride, 



after twenty-four hours' incubation, the most striking feature is 

 a general enlargement of all the bacilli. Sometimes in the 

 tissues they are seen to 

 be surrounded by an un- 

 stained capsule, though 

 this appearance is by no 

 means common. They 

 do not form spores. 

 Gordon, who has found 

 that they possess flagella 

 which, however, stain 

 with difficulty, states 

 that they are motile. 

 Most observers, however, 

 and with these we agree, 

 have failed to find evi- 

 dence of true motility. 

 They stain readily with 

 the basic aniline stains, FIG. 147. Bacillus of plague in chains show- 

 but are decolorised by {j^JJ^ 1 " 1111 * From a young culture 

 Gram's method. Stained with thionin-blue. x 1000. 



Cultivation. From 



the affected glands, etc., the bacillus can readily be cultivated 

 on the ordinary media. It grows best at the temperature of 



