CULTIVATION OF PLAGUE BACILLUS. 41 3 



fairly numerous, occurring chiefly in small clumps. They 

 occur also in the blood, in which they may be found 

 during life by microscopic examination, chiefly, however, 

 just before death in very severe and rapidly fatal cases. In 

 many cases, however, they cannot be detected in the blood 

 by this means, though in some of these they may be obtained 

 by means of cultures. 



Cultivation. From the affected glands 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 1 8 C. On agar and on blood serum the colonies 

 are circular discs of somewhat transparent appearance and 

 smooth shining surface. When examined with a lens, their 

 borders are 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. In peptone gelatine, growth takes place along 

 the needle track as a white line, composed of small 

 spherical colonies, whilst on the surface of the gelatine 

 a thin semi-transparent layer is formed, which may spread 

 to the wall of the tube. In bouillon the growth forms a 

 slightly granular or powdery deposit at the foot and sides 

 of the flask, somewhat resembling that of a streptococcus. 



In cultures, the organisms present the characters described 

 above, but as the cultures become older a great many swollen 

 and irregular forms are seen. 



The organism in its powers of resistance corresponds 

 with other spore-free bacilli, and is readily killed by heat. 

 It resists drying for four days at latest, and exposure to 

 sunlight for three or four hours kills it. When cultivated 

 outside the body the organism rapidly loses its virulence. 



Experimental Inoculation. Rats, mice, guinea-pigs, and 

 rabbits are susceptible to inoculation. After subcutaneous 

 injection there occurs a local inflammatory oedema, which 

 is followed by inflammatory swelling of the lymphatic glands, 

 and thereafter by a general infection. The animals die 

 usually in from one to five days, the chief changes, in addition 

 to the glandular enlargement, being congestion of internal 



