﻿STUDIES IN PLAGUE IMMUNITY. 245 



highly immunized and in which the blood also showed no agglutination 

 will not be given. The reactions were all performed with the virulent 

 strain, excepting in a few instances when it is so stated, and by the 

 macroscopic method. One oesc of the bacteria was suspended in 1 cubic 

 centimeter, 0.85 per cent saline solution and 1 cubic centimeter of the 

 serum to be tested, diluted with saline solution, was added to the suspen- 

 sion. It is perhaps unnecessary to state that the microscopic method of 

 observing agglutination with the plague bacillus is entirely untrustworthy. 



DETAILS OP THE EXPERIMENTS. 



Monkey number 1231. — Vaccinated October 10 with 1 culture "Pest Avirulent." 

 Reinoculated October 20 by tli rusting beneath the skin a 5 cubic centimeter 

 syringe needle which had been dipped in a suspension of "Pest Virulent." On 

 October 28, 1 oese "Pest Virulent" was inoculated subeutaneously ; on November 16 

 the animal was killed, and the agglutination of the serum tested in dilutions 

 1: 2 and 1:4; two controls of the reactions (of the bacterial suspension without 

 serum) were performed. All were negative after one and four hours. 



Rabbit number 1960. — May 11: One 48-hour slant culture of "Pest Avirulent" 

 in 1 cubic centimeter of bouillon was injected intravenously. The agglutination 

 was tested twelve days later in dilutions of 1 : 20, 1 : 40, 1 : 80, 1 : 1C0, 1 : 320, two 

 controls of the reaction (of the bacterial suspension without serum) were 

 prepared. All the reactions were negative after one and three-fourths hours. 

 After sixteen hours, pseudo-reactions in dilutions of 1 : 20 to 1 : 00 were observed, 

 the bacteria being precipitated and the suspensions appearing clear; the two 

 control reactions were negative. The serum was again tested on the following- 

 day in dilutions of 1: 40, 1: 80, 1: 100, with two controls. The reactions were 

 all negative after one hour. After sixteen hours, pseudo-reactions in the dilution 

 of 1 : 40 were observed. Three days later the serum was again tested in dilutions 

 of 1 : 5 and 1: 10 and two controls (without serum). The results were negative 

 after one and one-half hours. After sixteen hours pseudo-reactions in dilutions 

 of 1 : 5 and 1: 10 were observed; both controls were negative. 



Normal rabbit's serum was tested on this same date in dilutions of 1:5 

 and 1 : 10, with two controls of the bacterial suspension. All were negative after 

 one and one-half hours. After sixteen hours pseudo-reactions in dilutions of 

 1: 5 and 1: 10 were observed; both controls were negative. 



Rabbit number 1961. — May 12: One 48-hour culture of "Pest Avirulent," sus- 

 pended in 1 cubic centimeter of bouillon, was injected intravenously. Twelve 

 days later the animal was killed and the agglutination tested in dilutions of 

 1: 20, 1: 40, 1: 80, 1: 100, 1: 320. Three controls of the reactions without serum 

 and 1 control with normal rabbit serum in a dilution of 1 : 30 were performed. 

 After one hour pseudo-agglutination was observed in the dilutions of 1 : 20 and 

 1:40. The remaining tubes were all negative; after sixteen hours pseudo- 

 reactions took place in dilutions of from 1 : 20 to 1 : 80. The same serum tested 

 the following day in dilutions of 1 : 2 gave no agglutination after one and one-half 

 hours. 



Rabbit number 1963. — Inoculated intravenously with 5 cubic centimeters of 

 Haffkine's prophylactic. Five days after the inoculation the animal was killed 

 and the agglutination tested in dilutions of 1 : 2 and 1 : 5, with two controls. 

 The results were negative after two and sixteen hours. 



Rabbit number 1965. — Inoculated with 5 cubic centimeters of Haffkine's prophy- 

 lactic intravenously. Ten days later the animal was killed and tbe agglutination 



