468 A MANUAL OF BACTERIOLOGY 



Bacilli were first observed in this disease in the blood, 

 buboes, and organs by Kitasato in 1894. In the same 

 year (1894) Yersin investigated the outbreak of bubonic 

 plague at Hong Kong, and described the bacillus met with 

 in the buboes and its cultural and pathogenic properties 

 very fully. This organism is known as the Bacillus pestis. 



Morphology. The B. [Pasteurella] pestis belongs to the 

 group of hsemorrhagic septicsemic bacilli (chicken cholera, 



s-:- / 



* i 



3:" 



I 







FIG. 44. Smear preparation from spleen of inoculated guinea-pig. X 1 ,000. 



rabbit and ferret septicaemia, swine plague, etc., see 

 p. 481), and is a markedly pleomorphic organism. In 

 the animal body it occurs for the most part as a short, 

 plump rod, measuring 2-3 /^ by 1-2 /z, but longer forms 

 may be seen here and there measuring as much as 5 p, 

 (Fig. 44). Polar staining is a marked feature (Plates XIV, c, 

 and XV, a), and swollen involution forms occasionally occur. 

 The typical form of the organism, the bi-polar-staining, 

 short, stumpy bacillus, is met with in smears from the 

 buboes, in the sputum in the pneumonic form, and in the 



