104 ORIENTAL PLAGUE chap. 



produced (both in the guinea-pig and rat) with the 

 smallest trace of plague material, and moreover that by 

 which the virulence best asserts itself in the rat. The 

 plan which I employ is to scrape off the superficial 

 epidermis, in the guinea-pig at the inguinal mammary 

 teat, in the rat at the root of the tail, and, after slightly 

 and superficially scarifying the exposed surface, to rub in 

 lightly the material — culture or organ juice, as the case 

 may be. Subcutaneous injection, when adopted, is of 

 course performed in the groin. Whether cutaneously or 

 subcutaneously injected, the result, if positive, consists in 

 the formation of a tumour in the groin, swelling of the 

 inguinal glands, and hsemorrhagic oedema of the tissues 

 around. If the rat be cutaneously inoculated at the root 

 of the tail, the site of the resulting inguinal bubo depends 

 whether the inoculation is lateral or median. In the 

 former case the bubo develops on the side of inoculation, 

 in the latter the bubo develops in both groins. A lethal 

 dose of normal virulent B. pestis is the one which suffices 

 to kill a rat in thirty-six to seventy -two hours. 



The shortest duration of the fatal illness in rats occurred 

 in thirty-six hours; it was observed after cutaneous inocula- 

 tion at the root of the tail, with a twenty-four hours' agar 

 surface culture; a turbid emulsion was made, and of this a 

 droplet was rubbed into a few superficial scratches. In most 

 of the cases of control rats used by me in connection with 

 the experiments on my new plague prophylactic, the fatal 

 illness occurred between thirty-six and forty-eight hours, 

 so that the culture used must be pronounced of great, 

 i.e. normal, virulence. 



On post-mortem examination of the infected rat the 

 inguinal glands are found enlarged and deep red, and, as 



