rx PEOTECTIVE INOCULATION 275 



cutaneously at the same time and with the same material 

 died from typical acute plague in thirty-six to seventy-two 

 hours. 



(5) As is well known, guinea-pigs are less susceptible 

 to plague than white rats, the latter being, of all the 

 rat races which I have experimented with, the most 

 susceptible to plague. In the case of the guinea-pig a 

 dose of 20 milligrammes of the prophylactic now in question 

 twice injected at intervals of ten to fourteen days does 

 not afford protection in more than 50 per cent of the 

 animals ; the remainder die on subsequent injection with 

 virulent material of plague, though their death is delayed 

 several days (death in nine to twelve days or later), and 

 they show in the great majority of instances suppurating 

 bubo. The disease induced in these animals differs, how- 

 ever, from the subacute plague in an unprotected (control) 

 guinea-pig as follows : — (a) There is but slight enlarge- 

 ment of the spleen, with few necrotic nodules ; (b) the 

 liver contains either no necrotic nodules, or such nodules 

 only very sparingly ; (c) there is scarcity of B. pestis in 

 the bubo and in the spleen — in unprotected guinea-pigs 

 dead of subacute plague these two tissues being crowded 

 with B. pestis ; and (d) there is much greater amount of 

 necrosis in the lungs, the necrotic parts being packed with 

 B. pestis. It seems, therefore, that while in the un- 

 protected guinea-pig the bubo, spleen, and liver are more 

 involved and richer in B. pestis than in the protected 

 guinea-pig, the reverse is the case as regards the lungs. 



In the experiments which in 1899 I along with Dr. 

 Haffkine made with his prophylactic, and in the experi- 

 ments which I have repeatedly made since with Haffkine 

 prophylactic as prepared by myself, it was shown that for 



