﻿VII. SUMMARY OF THE RESULTS OF THE ANIMAL 



EXPERIMENTS IN IMMUNIZATION BY 



THE DIFFERENT METHODS. 



It will be seen from a study of the different series of experiments 

 described on pages 187 to 234 that in many instances the results in 

 immunization obtained by the same method of inoculation show con- 

 siderable variation. This is particularly so in the series of monkeys 

 inoculated in the early part of the work where the immunity of the 

 animals in the different series was tested with varying amounts of 

 the virulent pest organism. However, many difficulties were also en- 

 countered in the series in which the experiments were performed later. 

 In the beginning of this article and in the records of some of the 

 experiments, attention was called to the fact that the lethal dose for 

 the species of monkeys employed varied considerably. In some instances 

 over fifty times the lethal dose for one animal will not cause the death 

 of another of about the same size. For this reason and because occa- 

 sionally, in the earlier experiments, a control animal did not succumb 

 to pest infection, a very large -multiple of the lethal dose for the average 

 monkey was finally employed; therefore, the percentage of these animals 

 immunized was not as high as it might otherwise have been. It is undoubt- 

 edly for this reason that so low a percentage of the monkeys which had 

 previously been inoculated with killed cultures of the pest organism 

 subsequently resisted the infection. On the other hand, in my experi- 

 ments with guinea pigs inoculated with killed cultures, the percentage 

 of immunity obtained was as high as or higher than that frequently 

 encountered by other authors. 



Owing to this great individual variation in the susceptibility of 

 different monkeys to pest infection, a fact discovered during the course 

 of the inoculations, these animals did not prove to be as suitable as 

 guinea pigs for the comparison of the value of the different methods. 

 However, on the other hand, as has been mentioned above, the behavior 

 of the monkey in relation to its resistance and immunity to pest 

 infection probably much more closely resembles that encountered in man. 



It is obvious that the series of inoculations which have been described 



are not selected as ideal ones. The entire number performed in relation 



to immunization by the different methods has been recorded in the 



order in which the experiments were carried on, the unfavorable as 



55670 6 235 



