20 ORIENTAL PLAGUE chap. 



When a guinea-pig is injected intraperitoneal! y with a 

 trace of virulent B. pestis, the animal is found dead 

 within twenty-four to thirty hours ; the peritoneal cavity 

 contains a quantity of grey slimy exudation, which, under 

 the microscope, is made up of a sticky, viscid ground 

 substance in which are embedded densely packed B. pestis, 

 singly, in dumb-bells, and short chains. In stained film 

 specimens the bacilli appear surrounded, though somewhat 

 irregularly, by a faintly stained broader or narrower 

 capsule ; this is the gelatinous ground in which the bacilli 

 are suspended (see Fig. 26), but it is by no means 

 comparable to a typical capsule such as surrounds the 

 Diplococcus pneumonia. As will be mentioned later, the 

 B. pestis forms on the surface of solidified agar a slimy 

 translucent layer ; when a particle of it is removed with a 

 platinum needle it is viscid and is easily drawn out into 

 threads ; it does not emulsify readily, because the plague 

 bacilli are agglutinated together into larger or smaller 

 masses by a viscid hyaline intercellular secretion ; stained 

 film specimens show this intercellular substance faintly 

 stained, but this is not comparable to a real capsule. In 

 gelatine-surface cultures the growth of B. pestis is devoid 

 of this slimy character, the plague bacilli emulsify more 

 readily in salt solution, and there is in film specimens of 

 such emulsion no capsule recognisable. 



From all this it follows that the B. pestis does not 

 possess a real capsule such as is possessed by Diplococcus 

 pneumoniae. 



(B) Cultural Characters. — The plague bacillus grows 

 well at 37° C. ; it grows also well, but slower, below 37° C. 

 down to 20° C. and less. There seems a misunderstanding 

 on the part of Professor Simpson in saying, in his Treatise 



