﻿326 STRONG. 



be a much more delicate and accurate means of demonstrating the exist- 

 ence of an immunity reaction following plague vaccination, than those 

 already described. The experiments were performed with the strain 

 "Pest Virulent" in the following manner : 



The blood was collected 10 days after vaccination. 0.1 cubic centimeter 

 of the serum, 0.1 cubic centimeter of a suspension of a normal guinea pig's 

 washed leucocytes and 0.1 cubic centimeter of a suspension of the strain "Pest 

 Virulent" were thoroughly mixed and the resulting suspension placed for thirty 

 minutes at 37° C. Smears were then prepared and stained and 200 leucocytes 

 counted. Control experiments of the nonphagocytic power of the washed leuco- 

 cytes without serum were always prepared. 



Series 62 (p. 267) shows the opsonic index both before and after vac- 

 cination. No attempt was made by frequent examination, to demonstrate 

 a negative phase immediately following vaccination or to plot the curve of 

 the reaction. As the table demonstrates, there was usually a distinct 

 increase in the opsonic index following the inoculation, but this was not 

 invariably the case. The increase in the opsonic action of the blood in 

 animals immunized against plague has already been discussed under the 

 subject of the immunizing" action of plague immune sera. (See p. 265.) 



The most satisfactory test of the demonstration of the immunity re- 

 action in the blood of the vaccinated individuals was obtained from a 

 study of the action of the serum in relation to the phenomenon of fixa- 

 tion of the complement after the method of Bordet and Gengou. These 

 experiments have .already been referred to under the discussion of the 

 mechanism of the action of plague immune serum. Hemolytic sera 

 were first prepared by inoculating rabbits with goats' corpuscles; these 

 were then collected from the rabbits, inactivated, and their hemolytic 

 power for a 5 per cent suspension of serum-free goat's corpuscles 

 carefully determined. Fresh guinea pig serum was used to furnish the 

 complement, and the minimum amount of complement for the reaction 

 also ascertained. The human serum to be tested for plague immune 

 bodies was then inactivated by heating for one hour at 56° C. A suspen- 

 sion in saline solution of a 24-hour agar culture of the virulent pest strain 

 which was free of all clumps was employed. The experiments were 

 performed in the following manner : 



One cubic centimeter of the diluted human inactivated serum from the vac- 

 cinated person was added to 1 cubic centimeter of the suspension of bacteria and 

 the unit dose of complement mixed with it. After one hour at 37° C, twice the 

 dissolving dose of inactivated rabbits' serum specifically hemolytic for goats' 

 corpuscles and suspended in 1 cubic centimeter saline solution and 1 cubic 

 centimeter of the 5 per cent solution of goats' corpuscles was added and the 

 mixtures placed at 37 ° C. for 2 hours. At the end of this time the reactions were 



