iv MICROBES SIMULATING THE B. PESTIS 83 



on the rat, do not cause in the guinea-pig or in the mouse the large 

 firm spleen characteristic of plague; they do not form the "granular" 

 irregular conical colonies on gelatine as B.pestis does. On agar they 

 form more or less flat colonies. They make broth turbid and form 

 indol. Injected into the veins of rabbits the members of this group 

 cause death within twenty hours ; B. pestis in this way administered 

 does not cause death before two or three days or later. As is also 

 well known, bacillus of fowl cholera subcutaneously injected causes 

 death of rabbits and pigeons in less than two days. The B. equi, 

 however, takes much longer in the rabbit (four days), causing pseudo- 

 membranes on the viscera, and is non-pathogenic to the pigeon. From 

 this it is evident that a diagnosis would have to take account of the 

 morphological and cultural, as well as the experimental data. A 

 mistake would, however, be possible if diagnosis were made, for 

 instance, on morphological grounds alone, e.g. non-motility, bipolar 

 staining, and being Gram-negative ; or say, on the ground of the 

 nature of an agar culture, forming a translucent cohesive film on the 

 surface of the agar ; or, say, by its subcutaneous action on rodents. 



Kister and Schmidt (Centralbl. f. Bakt. und Parasit. vol. xxxvi. 

 p. 454) found in some rats dead on board ship a microbe which 

 showed bipolar staining and which belonged to the group of bacteria 

 causing haemorrhagic septicaemia. The peculiarity of the microbe of 

 these observers was, that it proved virulent even for rats and cats. 

 It was highly virulent for other rodents. 



