﻿STUDIES IN PLAGUE IMMUNITY. 



267 



strate the negative phase of the reaction or to plot their curves, and as 

 the normal opsonic action is known to vary considerably from time to 

 time, this may account for the apparent absence of the increase of the 

 index in some of the cases at the time of the examination of the serum. 

 Moreover, the reaction may not in some instances have reached its maxi- 

 mum or it may in others have begun to decline. However, the general law 

 may be determined from the study of the entire series of experiments. 



In conclusion it may then be stated that plague immune serum acts 

 neither as an antitoxic serum nor as do other bactericidal sera, but its 

 action may be said to be anti-infectious and opsonic in nature. 



EXPERIMENTS. 



Series 61. — Determination of the opsonic index in guinea pigs. 



The animals were inoculated with 1 cubic centimeter of a suspension of the 

 strain "Pest Virulent" in saline solution. Thirty-five minutes to one and one-half 

 hours after the injection, drops of the abdominal fluid were drawn off and smears 

 prepared and stained. The average number of bacteria contained in fifty leu- 

 cocytes was then counted. Unfortunately, the opsonic index was not determined 

 before the animals were vaccinated and therefore the experiments were performed 

 in normal as well as in vaccinated animals. 



Animal No. 



1977 (vaccinated) ._ 



2273 (normal) 



1980 (vaccinated) 



2282 (normal) 



2154 (vaccinated) 

 2162 (vaccinated) 

 2861 (normal) 



How immunized. 



Vaccinated with 2 cultures "Pest Avirulent." Immunity 

 tested later. 



Vaccinated with 2 cultures "Pest Avirulent." Immunity 

 tested later. 



1 agar slant "Pest Avirulent." Immunity tested later . 

 do 



Opsonic in- 

 dex of strain 

 "Pest Viru- 

 lent" after 

 li hours. 



11.3 



9 



8 



4.6 



8 



5 



Series 62. — Determination of the opsonic index in human beings, guinea pigs 



and monkeys. 



This series comprised the examination of the opsonic index in both human 

 beings and animals vaccinated against pest. The opsonic index was tested against 

 the strain "Pest Virulent" both before and after the immunization. In a few 

 instances, after immunization, the opsonic index was also tested with two other 

 strains of the pest bacillus, as may be seen from the table. One-tenth cubic 

 centimeter of the serum, 0.1 cubic centimeter of a thoroughly washed suspension of 

 guinea, pig's corpuscles, and 0.1 cubic centimeter of a suspension of the organism 

 "Pest Virulent" were thoroughly mixed and the resulting suspension placed at 

 37° C. for thirty minutes. Smears were then prepared and stained, two hundred 

 leucocytes being counted. 

 55670 8 



