﻿260 STRONG. 



The success of the reaction in experiments of this nature, providing 

 of course that the serum to be tested possesses a bactericidal power, 

 obviously depends upon the selection of an animal serum containing 

 complement with receptors suitable to unite with the amboceptors in the 

 immune serum. As bas been mentioned, Kolle and Hetseh in their 

 experiments employed the sera of the pigeon, cow, horse, chicken, rabbit, 

 donkey, and rat to furnish the complement. 



However, it was demonstrated by the following additional experiments 

 that my failure, in the experiments which I have just described, to obtain 

 a bactericidal reaction or to demonstrate any other injurious effect on 

 the plague bacillus resulting from the action of the pest immune serum 

 on this organism was not due to the fact that I had not found a suitable 

 complement for the amboceptors. 



A horse's pest immune serum (not inactivated), which at the time 

 in doses of 1 cubic centimeter n-as able to protect against fatal pest 

 infection about 90 per cent of the rats inoculated with it, was mixed with 

 perfectly fresh rat serum and its bactericidal value tested according to 

 the method, in vitro, which has already been described. In order that 

 the phenomenon of the deflection of the complement by amboceptors, as 

 described by Neisser and Wechsberg, might not interfere with the reac- 

 tion, the experiments were also performed with varying amounts of the 

 horse's immune serum and fresh rat serum. However, no difference could 

 be detected between the results obtained with these experiments and 

 with those performed in the same manner with normal horse serum plus 

 fresh rat serum. 



These experiments and those of Kolle and Hetseh already outlined 

 appear to demonstrate that the pest immune serum which is known to 

 possess anti-infectious power in the animal, possesses in vitro no bacte- 

 ricidal action whatever, that is similar to that possessed, for example, by 

 tyjjhoid immune serum. It is also clear that the pest bacilli are not 

 only not killed by the immune serum, but that they- remain alive and are 

 capable of subsequent development. Therefore, it is evident that some 

 other factor must play an important role in the ultimate destruction of 

 the inoculated bacilli in the body of an animal either passively im- 

 munized by the injection of such a serum or actively immunized by 

 vaccination, and according to the conceptions of Metchnikoff it might be 

 argued that since the serum in the test tube is apparently without injurious 

 action upon the pest bacilli, the phagocyte must be the additional factor 

 which is necessary to render harmless and to destroy the organism in 

 question. 



However, before accepting this hypothesis, it seemed advisable further 

 to investigate not only what action the serum has upon the life of the 

 plague organism, but also what action the organism lias upon the 



