﻿STUDIES IN PLAGUE IMMUNITY. 259 



substances such as an aggressin, in the sense in which Bail uses the term, or by 

 assuming that the bacteria which appeared later in the abdominal cavity, sur- 

 rounded by capsules, possessed a negative chemotactic action. Possibly both 

 of these factors played a role, although he was unable to determine the question 

 definitely. He also found, as Denys and Tartakowsky had done, that where 

 immune serum was injected into the abdominal cavity of a guinea pig, shortly 

 after the introduction of the organisms, phagocytosis in addition to agglutination 

 of these bacteria of the second generation occurred. 



After a study of the experiments which had been performed in relation 

 to the bactericidal action of the pest immune serum in vitro, it appeared 

 to me, to judge from the careful experiments of Kolle and Hetsch on pest 

 immune serum, that this question was definitely settled as far as the 

 methods employed were concerned. The experiments of Wright and Lamb 

 and my own already referred to, relating to the bactericidal reaction in 

 vitro of normal human and other mammal's blood, also appeared conclusive. 

 However, in order further to complete the evidence, the following addi- 

 tional exjjeriments, consisting of the examination of the bactericidal power 

 of horse's perfectly fresh pest immune serum, as compared with horse's 

 fresh normal serum, were undertaken. I also studied the bactericidal 

 power of horse's inactivated pest immune serum, after the addition of 

 perfectly fresh monkey serum to supply the complement. The horse's 

 immune serum in the latter instance was inactivated by heating for one 

 hour at 56° C. The experiments were performed in the following way: 



In test tube I were placed 1 cubic centimeter of perfectly fresh, horse's immune 

 serum (without the addition of carbolic acid) -+- 1 cubic centimeter of a suspen- 

 sion of an agar culture of the virulent pest bacillus in bouillon, in a dilution of 

 1 to 50,000. 



In test tube II were placed 1 cubic centimeter of perfectly fresh, normal 

 horse serum + 1 cubic centimeter of a suspension of an agar culture of the 

 virulent pest bacillus in bouillon in a dilution of 1 to 50,000. 



After thorough mixing of the contents of each tube they were both placed for 

 three hours in the incubator at 37° C, when sets of agar plates were prepared. 

 No difference in the bactericidal action of the two sera could be distinguished. 



In the second series of experiments, in test tube I were placed 1 cubic 

 centimeter of the inactivated, horse's immune serum + 0.5 cubic centimeter of 

 the suspension of the bacilli + 0.5 cubic centimeter of monkey's fresh normal 

 serum in a dilution of 1: 10. 



In test tube II were placed 1 cubic centimeter of horse's inactivated, normal 

 serum + 0.5 cubic centimeter of a suspension of the bacilli + 0.5 cubic centi- 

 meter of monkey's fresh, normal, serum in a dilution of 1 : 10. 



In test tube III were placed 0.5 cubic centimeter of the supension of the 

 bacilli + 1.5 cubic centimeters of saline solution. 



In test tube IV, 0.5 cubic centimeter of a suspension of the bacilli + 0.5 

 cubic centimeter monkey's normal serum + 0.5 cubic centimeter saline solution. 



These experiments were performed in dilutions of the serum of 1:2, 

 1 : 10, 1 : 100, and 1 : 500. No marked difference could be discovered in 

 the number of colonies in the plates prepared from the suspensions of 

 immune serum and from that of the normal serum. 



