ii CHARACTERS OF THE B. PESTIS 31 



(bubo, blood, spleen) or into an emulsion of a recent 

 culture of B. pestis (twenty-four hours' agar culture at 

 37° C.) a few scratches or superficial scarifications are 

 made, or the surface cuticle is scraped off from the place 

 bared of the hairs and slightly scratched with the point 

 of a knife ; then a particle of growth from an agar 

 culture (twenty-four hours at 37° C), having been removed 

 from the culture with a platinum loop, or a particle of 

 plague tissue, is directly rubbed in by the platinum loop 

 or the scalpel respectively into the scratched skin. 

 Provided the culture be of medium virulence, I have in a 

 very considerable number of experiments never failed by 

 ihis method to obtain positive results in mice and rats — 

 ;hat is, acute plague with fatal issue. According to the 

 drulence of the culture, fatal issue, both in mice and in rats, 

 Follows in as short a time as 30-40-48 hours ; or, working 



r ith less virulent culture, death may be delayed up 

 ;o four or five days. In mice such delay is, however, 

 •are even with less virulent culture, since mice are 



Lighly susceptible and promptly answer even to plague 

 materials which, when tested on rats, and particularly 

 on guinea-pigs, appear only of moderate virulence. 



Subcutaneous injection of mice and rats with doses 

 much larger than are required for cutaneous inoculation 

 does not cause quicker or more virulent results than 

 cutaneous inoculation. It is otherwise with guinea-pigs : 

 subcutaneous injection, while permitting the application 

 of larger doses than does the cutaneous inoculation, causes 

 — if the virulence is not abnormally low — fatal issue in 

 between two and three days ; material which acts thus 

 may be considered of normal virulence. Death in less than 

 forty-eight hours in a guinea-pig after subcutaneous injec- 



