﻿STUDIES IN PLAGUE IMMUNITY. 179 



only a small percentage of these animals by such a process. The guinea 

 pigs comprising Series 50 were inoculated with the killed agar cul- 

 tures, chiefly for the purpose of comparing this method with the other 

 methods of inoculation which were being tested at the same time. 



In all, fifteen guinea pigs and seventy-tbree monkeys were inoculated 

 with killed cultures of the pest bacillus; 26 per cent of the guinea pigs 

 and 32 per cent of the monkeys subsequently proved to be immune. 

 However, if Series 23 is excluded- as it should be, since probably both 

 killed and living organisms were used in the immunization of the animals, 

 the percentage of immunity in the remaining monkeys is but 25 per 

 cent. 



2. inoculations in animals with living attenuated cultures 



(vaccination). 



I have recently 41 reviewed the literature regarding the early experi- 

 ments made to attenuate virulent strains of the pest bacillus and of the 

 inoculations performed in animals with other avirulent strains of this 

 organism, and it is not my intention here to enter into any lengthy dis- 

 cussion of this subject but merely to mention these experiments. 



The German Plague Commission made some attempts at attenuating strains 

 of the pest bacillus for use in immunization, by exposing the living cultures 

 both to a temperature of 51° C. for varying periods of time and also to the 

 action of carbolic acid. These experiments resulted unsuccessfully, the organisms 

 retaining their full virulence. Albrecht and Gohn a and Yersin and Carre 4 ' 1 

 also performed experiments on guinea pigs, rats and monkeys with somewhat at- 

 tenuated pest cultures. No extensive or convincing experiments in regard to the 

 value of the living, attenuated cultures in the immunization of animals against 

 plague had apparently been undertaken until Kolle and Otto investigated this 

 subject. These authors, in numerous and careful experiments on rats and guinea 

 pigs, showed that cultures of the pest bacillus so attenuated that they were no 

 longer dangerous to these animals even in large amounts (2 agar cultures) were 

 capable upon injection of giving rise in them to a much higher immunity than 

 was produced by the killed cultures of the organism. Thus, in one series of 

 fifty-nine guinea pigs which were immunized by a single inoculation of an 

 attenuated living culture, thirteen died and two were killed for control purposes. 

 On testing the immunity of the remaining forty-four from three to eight months 

 after their vaccination, twenty-eight, or 63.0 per cent, remained alive. 



In another series of thirty-four guinea pigs immunized with an attenuated 

 pest culture (Maassen V), of which one died during the process of immunization, 

 twenty-one were reinoculated with the virulent organism from one to four months 

 after their vaccination, and of this number, sixteen (70 per cent) remained 

 alive and five died. Nine other guinea pigs were inoculated with this, agar 

 culture and at the same time with plague immune serum.- All proved to be 

 immune upon reinoculation with the virulent pest bacillus. 



41 This Journal (1900), 1, 182. 



42 hoc. cit. 



43 Congress International de Med. Section de Med. et Chirug. Militaires. Sons 

 section Coloniale Paris (1004), 54. 



