ii CHAEACTERS OF THE B. PESTIS 29 



it need not, on account of the delay and the above 

 difficulties, be considered as essential, and also because 

 there are other quicker means of establishing positive 

 diagnosis. 



Hankin describes a modification of the B. pestis when 

 growing in salted media, viz. that the bacilli grow out 

 into long filaments. I have many years ago 1 described 

 such filamentous modification occurring in many microbes 

 (coli-typhoid group and others) when growing in media to 

 which more than the normal amount of salt is added, and 

 I cannot therefore accept either Hankin's priority (gener- 

 ally attributed to him in this matter) nor that such 

 filamentous change is characteristic for B. pestis. 



(C) Experimental. — B. pestis produces in rodents after 

 cutaneous or subcutaneous injection definite disease. This 

 will be considered in detail later on, here we wish merely 

 to give a general account of its action. 



A loopful, or even a part of a loop, of a 24 h. culture 

 on agar at 37° C, or a trace of plague material (bubo, 

 spleen) containing a large number of B. pestis, injected 

 into the peritoneal cavity of a young or half-grown guinea- 

 pig, causes fatal results in twenty to thirty-six hours, if the 

 B. pestis is of normal virulence ; if the dose is too small 

 or the virulence subnormal, death may be considerably 

 delayed. In the former case the abdominal organs are 

 found much congested, with petechise on the serous 

 covering of the intestine and on the parietal peritoneum ; 

 in the peritoneal cavity is copious, sticky, viscid grey 

 exudation ; under the microscope, besides red blood 

 corpuscles and a few leucocytes — the number of the latter 



1 Klein, Grouse Disease and Fowl Enteritis, 1892, p. 31 ; Micro-organisms and 

 Disease, new edition, 1896, p. 93. 



