44 



This irregularity does not generally occur in the case of a serum 

 derived from an animal which has been strongly immunised by 

 weekly series of inoculations; it may possibly be ascribed to 

 the single inoculation. 



After an interval of three months the weekly injections of 

 heated culture were continued for six weeks : at the end of the 

 treatment the agglutination titre was up to 1 in 160. The 

 inoculation of living culture was then begun for the first time, 

 0.5 c.c. of broth culture being administered subcutaneously. 

 The doses were increased up to 5 c.c. intravenously, when the 

 animal died at the end of the 3rd week, six days after the last 

 inoculation. The post-mortem examination revealed large vege- 

 tations on the cusps of the mitral valves, and diplococci were 

 demonstrated in the blood. 



The blood serum, collected while the animal was moribund, 

 had an agglutination titre of 1 in 320, and in doses of 0*2 c.c. 

 conferred protection on mice against 0-01 c.c. of broth culture 

 of the homologous type, the fatal dose of which was 0-000 000 001 

 c.c. The interpretation of this result has been discussed on 

 page 40. 



Disappearance of Pneumococci in Passively Immune Mice. 



Many careful and elaborate investigations have been made 

 by others on the disappearance of pneumococci from protected 

 mice with the object of explaining the mode of action of the 

 immune serum. The following observations illustrate a few 

 particular points and are in no way an attempt to deal exhaustively 

 with the subject. 



Mice were protected by the intraperitoneal injection of 

 0-2 c.c. of a Group IV serum. The following day, a number of 

 the mice received the dose of 0*1 c.c. of the homologous culture 

 given intraperitoneally. After an interval of one hour, a protected 

 mouse and a control mouse, which had received culture only, 

 were killed. Smear preparations from each of the two showed 

 in the peritoneal cavity numerous pneumococci, which in the 

 protected mouse were in clumps. Plate cultures also were made 

 from the blood : from the unprotected mouse numerous colonies 

 were grown, while the plate from the blood of the protected 

 mouse remained sterile. The blood of the latter animal, however, 

 did contain living pneumococci, since 0-5 c.c. of the blood sown 

 in broth produced a positive culture. A second mouse was alive 

 and well 48 hours later. It was killed, and cultures were made 

 from the blood and peritoneal cavity; all proved negative. 



Four of the remaining protected mice were inoculated sub- 

 cutaneously with 0' 1 c.c. of the homologous culture, in addition 

 to several unprotected controls. After 4 hours, one of each 

 series was killed ; in both cases smear preparations showed the 

 presence of capsulated diplococci at the seat of inoculation. 

 A protected mouse, killed after 24 hours, still showed living 

 pneumococci at the seat of inoculation, but the blood was 



