﻿STUDIES IN PLAGUE IMMUNITY. 177 



The most important and most convincing experiments in regard to the value 

 of immunization with killed cultures of the plague bacillus in rats and -guinea 

 pigs have been made by Kolle and Otto. 40 In their experiments the loss during 

 the process of immunisation of the rats with Haffkine's prophylactic was 38.5 

 per cent and with the killed agar cultures 33.3 per cent. 



Later, on testing the immunity of the animals remaining alive, it was 

 found that only 21.9 per cent of those which had been inoculated with the 

 killed agar cultures, and but 22.2 per cent of those inoculated with Haffkine's 

 prophylactic, gave evidence of an acquired immunity by surviving the test. 

 Attempts were made to immunize 26 guinea pigs with killed agar cultures, 

 amounts as large as from i to 1 entire agar culture being injected subcutaneously. 

 During the process of immunization four of the animals died. Of the remaining 

 twenty-two, only two (7.7 per cent of the whole) appeared to be immune on 

 subsequent testing. Hardly more favorable results were obtained in the experi- 

 ments in which killed bouillon cultures were employed. Twenty animals were 

 inoculated with Haffkine's prophylactic. Two of these died from the effects of 

 the immunization and of the remaining eighteen, only two (10 per cent) re- 

 mained alive after reinoculation with the virulent organism. Other experiments 

 on guinea pigs were also performed in which repeated inoculations were made 

 with killed cultures of the plague organism. The: animals were first injected 

 with 1, then with li and finally with 2 killed agar cultures or with 1,1-} and 3 

 cubic centimeters of Haffkine's prophylactic. In the process of immunizing 

 twenty guinea pigs by these methods, six of the animals died from the effects 

 of such large doses of the killed bacteria. The immunity of the remaining 

 fourteen was tested six weeks after the last injection with the living virulent 

 plague bacillus when only one animal remained alive and proved to be immune. 



Ill my own experiments the value of inoculation with killed cultures 

 of the pest bacillus was tested on monkeys and guinea pigs. 



ANIMAL EXPERIMENTS. 



A. With monkeys. — It seemed desirable to experiment furtber with 

 killed cultures of the pest bacillus for two reasons, first, to compare 

 the immunizing value of the dead organism with that of other methods 

 of inoculation, such as those of vaccination, natural and artificial aggressin 

 injections etc., and second to see whether sufficiently good results could 

 be obtained by experiments on Manila monkeys to warrant advocating 

 the use of this method in man. 



In Series 5, page 189 are given the results of the experiments on 

 eight monkeys inoculated witli killed bouillon cultures (Haffkine's 

 method) in varying amounts. On testing the immunity of these animals 

 by thrusting a syringe needle infected with virulent pest bacilli beneath 

 the skin, eleven days after the primary inoculation, only three were found 

 to possess sufficient immunity to survive the infection. Of those which 

 died, one had previously received 30 cubic centimeters and another 20 

 cubic centimeters of the prophylactic. From what lias been said under 

 the discussion of the susceptibility of this species of monkey to pest 

 infection, it will be seen that the method of testing the immunity of the 



40 Ztschr. f. ifyg. u. Iiifcciionskranlh., Leipz. (1903). 45, 512; (1904), 48, 399. 



