﻿STUDIES IN PLAGUE IMMUNITY. 



319 



Pfeiffer 121 found that in immunization against plague, the degree of immunity 

 produced depended not only upon the dose of the killed pest culture but also upon 

 the degree of virulence of the killed organism, and concluded that the immuniz- 

 ing effect of pest bacilli is, up to a certain extent, proportional to the virulence 

 of the culture employed. Kolle and Martini 122 found that the less virulent 

 strains of pest bacilli were agglutinated by an immune serum in higher dilutions 

 than more virulent ones. However, Shibayama 1 - 3 could not confirm this fact. 



. In my experiments in agglutination of pest bacilli, the strain "Pest 

 Avirulent" was agglutinated more easily than -"Pest Virulent/' but as 

 pseudo-agglutinations occurred so frequently with the former strain, I 

 am not willing to draw any conclusions from my experiments in regard 

 to tbis question. 



The pest bacillus is not a very favorable organism with which to study 

 the relation between virulence and immunizing power, and a particularly 

 unfavorable one with which to undertake binding experiments of the 

 amboceptors in an immune serum. Por this reason, I shall only briefly 

 discuss the results which were obtained in immunization with several of 

 the strains of different virulence. As may be seen from a number of the 

 taltles of inoculation, monkeys inoculated by thrusting subcutaneously a 

 syringe needle which had- been dipped in a suspension of the strain 

 "Pest Virulent," freqtiently survived the inoculation and later showed 

 themselves to be immune to pest infection. On the other hand, monkeys 

 inoculated in the same manner, with a suspension of the strain "Pest 

 Avirulent" always survived the inoculation, but later invariably showed 

 no demonstrable immunity, and all succumbed to pest when reinoculated 

 with a lethal dose of the virulent strain. 



Throughout the numerous experiments performed in the vaccination 

 of guinea pigs and monkeys with the strains "Pest Avirulent" and pest 

 "Maassen Alt," it became clearly demonstrated that the latter organism 

 was distinctly more virulent than the former. This fact may be con- 

 firmed from a study of the series of inoculated animals given in the tables, 

 and also from them it may clearly be seen that the strain pest "Maassen 

 Alt" produced a higher immunity in the animals which were inoculated 

 with it than was brought about in those inoculated with the strain "Pest 

 Avirulent." The following table summarizes these results : 



Strain of plague bacillus. 



Guinea pigs. 



Monkeys. 



Number 

 inocula- 

 ted with 

 1 agar 

 slant 

 culture. 



Number 

 died 

 from 

 inoc- 

 ulation. 



Percentage 

 found im- 

 mune on 



subsequent 

 test. 



Number 

 inoc- 

 ulated. 



Number 

 died 

 from 

 inoc- 

 ulation. 



Percentage 

 found im- 

 mune on 



subsequent 

 test. 



"Pest Avirulent".. 



60 

 47 



2 

 6 



68.6 



88 



44 

 49 



1 

 5 



52 



70 







12l Berl. Kiwi. Wchnsch. (1902), 39, 581. 

 122 Deutsche med. Wchnsch. (1902), 28, 45. 

 ™CentrM. f. Bakteriol. Orig. (1005), 38, 482. 



