﻿STUDIES IN PLAGUE IMMUNITY. 185 



4. IMMUNIZATION WITH PLAGUE AGGIiESSIN. 



Hueppe and Kikuchi were the first to perform experiments with 

 natural plague aggressin in animals and to announce that a certain and 

 not dangerous method had been discovered for immunization against 

 pest. This work has already been referred to in the introduction to 

 this article. Their experiments were few in number but the authors 

 mention that it was their intention merely to call attention to the 

 priority of the use of this method of immunization of animals against 

 plague. The guinea pigs which were immunized had received several 

 inocidations of the aggressin exudates. 



(a) IMMUNIZATION WITH ARTIFICIAL AGGRESSIN. 



Further attempts at immunization with the free receptors of the 

 plague bacillus (artificial plague aggressin) were being performed in 

 this laboratory at the time of the appearance of Hueppe and Kikuchi's 

 work, but no very favorable results could be obtained. After the publica- 

 tion of their article the subject was investigated anew, although I had 

 already made a preliminary report of the value of immunization with 

 artificial plague aggressin on March 3, 1906. 48 Further experiments 

 made in immunization with artificial plague aggressin are given in detail 

 in Series 29, 30, 31, 36, and 42 (pp. 223 to 229), together with the 

 method of preparation of the extract of the organism. In all, twenty-six 

 guinea pigs and thirty-two monkeys were inoculated with the extracts of 

 the strain "Pest Virulent." Only three of the guinea pigs (11 per cent) 

 and but four of the monkeys (12.5 per cent) proved to be immune, when 

 the immunity of the animals was tested from two to seven weeks after 

 the first inoculation. These results were so unfavorable as compared 

 with those in which the living, attenuated cultures of the pest organism 

 were used for inoculation, that this method was not pursued further, but 

 experiments with natural plague aggressin were undertaken on guinea 

 pigs for the purpose also of comparing the immunizing power of this 

 substance with that of the living attenuated organism. 



(6) IMMUNIZATION IN GUINEA PIGS WITH EXUDATES FROM PLAGUE-INFECTED 

 ANIMALS ( NATURAL AGGRESSIN ) . 



The protocols of the animals employed are given in Series 34 and 43 

 (p. 229), where the further details in the preparation of the aggressin 

 exudates are also described. Fifteen of the guinea pigs of Series 35 (p. 

 230), were inoculated with the exudates obtained from the animals com- 

 prising Series 34, the guinea pigs each receiving, intraperitoneally from 

 2 to 5 cubic centimeters of the exudates. All survived the inoculation of 

 the aggressin. Their immunity was tested with the virulent organism 

 about two months after the first inoculation, when all but four (26+ per 



48 This Journal (1906), 1, 501. 



