440 PLAGUE. 



ever, just before death in very severe and rapidly fatal 

 cases. In most 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 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 cultures on agar with a dry surface and 

 slightly alkaline reaction are incubated at the body 

 temperature involution forms rapidly appear. These are 

 well seen on the third day and present the most varied 

 forms rounded, oval, pyriform, etc. ; some reach a size 

 many times that of the healthy bacillus (Haffkine). In 

 stab cultures 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 is usually 

 restricted to the region of puncture, though sometimes it 

 may spread to the wall of the tube. In bouillon the growth 

 usually forms a slightly granular or powdery deposit at the 

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

 streptococcus. If, however, the flasks containing the 

 bouillon be kept absolutely at rest flakes form at the 

 surface, and from these growth extends downwards forming 

 the so-called " stalactites." The columns of growth are 

 easily broken when the flasks are moved, and then fall to the 

 bottom in the form of a powdery deposit. Haffkine con- 

 siders this feature along with the involution forms on dry 

 agar to be of great importance in the diagnosis of the 

 organism. 



The organism in its powers of resistance corresponds 

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



