392 A MANUAL OF BACTERIOLOGY 



At the commencement and at the end of an epidemic 

 the disease may assume an extremely mild type, the 

 so-called " pestis minor." 



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 



FIG. 43. Smear preparation from spleen of inoculated 

 guinea-pig, x 1000. 



with in the buboes and its cultural and pathogenic properties 

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

 Morphology. The B. pestis belongs to the group of 

 hsemorrhagic septicsemic bacilli (chicken cholera, rabbit 

 and ferret septicaemia, swine plague, etc., see p. 404), 

 and is a markedly pleomorphic organism. In the animal 

 body it occurs for the most part as a short, plump, non- 

 sporing rod, measuring 2-3 /m by 1-2 /u., but longer forms 

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

 (Fig. 43). Polar staining is a marked feature (Plate XIV. 

 a and 6), and swollen involution forms occasionally occur. 



