586 Plague 



Haffkine* found that when an inoculated bouillon cul- 

 ture is allowed to stand perfectly at rest, on a firm shelf 



Fig. 204. Bacillus pestis. Highly virulent culture forty-eight 

 hours old, from the spleen of a rat. Unstained preparation (Kolle and 

 Wassermann). 



or table, a characteristic appearance develops. In from 

 twenty-four to forty-eight hours, the liquid remaining limpid, 

 flakes appear underneath the surface, forming little islands 



Fig. 205. Bacillus pestis. Involution forms from a pure cul- 

 ture on 3 per cent, sodium chlorid agar-agar. Methylene-blue (Kolle 

 and Wassermann). 



of growth, which in the next twenty-four to forty-eight 

 hours grow into a jungle of long stalactite-like masses, the 



* "Brit. Med. Jour.," June 12, 1897, p. 1461. 



