240 OMENTAL PLAGUE chap. 



venous or subcutaneous injection, first of sterile and 

 then of living culture, nor repeated subcutaneous or 

 intravenous injection of Haffkine's prophylactic, pro- 

 duces germicidal substances in the blood of this 

 animal in appreciable amount and in a way to 

 render its serum serviceable for neutralising the fatal 

 effect upon the guinea-pig of a dose of living culture of 

 plague bacillus. It will have been noticed from the 

 above control experiments that the dose of plague 

 emulsion, viz. 100 cubic millimetres, generally used, was 

 by no means a large dose, since some of the control 

 guinea-pigs did not die, while in most instances death 

 was delayed. It will be remembered from my Eeport 

 1896-1897 that the normal fatal dose for a guinea-pig is 

 the one that kills a half-grown animal between forty- 

 eight and seventy -two hours. In the cases now in 

 question some of the (control) animals die as late as the 

 seventh or eighth day. 



(c) Rats. — One rat, which had been twice subcuta- 

 neously injected with Haffkine's prophylactic, November 

 21 and December 31, was killed on January 30. 



250 cubic millimetres of plague emulsion mixed with 

 250 cubic millimetres of blood serum of above rat were 

 injected into one rat, No. 1, and 



250 cubic millimetres of emulsion only into a control 

 rat, No. 2. 



Both animals died of plague, No. 1 on the fifth, No. 2 

 on the fourth day. 



A further experiment was the following : — 



A rat which had been protected by a first injection of 

 10 cc. of Haffkine's prophylactic was a week later injected 

 with an ordinarily fatal dose of living plague culture. 



