﻿266 STRONG. 



hours the animal is killed with chloroform. The abdominal exudate, if sterile, is 

 collected and mixed with an excess of 0.1 per cent of ammonium oxalate solution 

 in 0.85 per cent sodium chloride solution (as proposed by Simon, ) sr and thoroughly 

 centrifuged. The packed corpuscles are then washed several times in excess 

 of saline solution and each time recentrifuged. In performing the tests one 

 volume of leucocytes plus one volume of a saline suspension of the pest bacteria 

 plus one volume of the serum to be tested are thoroughly mixed and incubated 

 for thirty minutes at 37° C. After this time smears are prepared and stained 

 with methylene blue. Two hundred leucocytes were counted and the average 

 number of bacteria ingested determined. Control experiments with normal sera 

 of the same species of animal were prepared as well as a control showing the 

 nonphagocytic power of the washed leucocytes. The method of counting the 

 phagocytic cells as suggested by Simon rather than the number of bacteria in 

 each phagocyte as recommended by Wright, appears somewhat simpler and the 

 error of variation between repeated counts with it was in some instances not so 

 great. However, which of these methods will eventually prove to be the more 

 reliable in determining the actual opsonic index I am not prepared to state. 



A few experiments were also performed in determining the opsonic 

 action of vaccinated animals by another method which, however, was not 

 found to be as satisfactory as the one already described. 



In these experiments the animals to be tested were first inoculated intraperi- 

 toneally with a suspension of the strain "Pest Virulent" and after thirty-five 

 minutes to one and one-half hours, drops of the abdominal fluid were drawn off 

 and smears prepared and stained. The average number of bacteria contained in 

 50 leucocytes was then counted. 



While the animals which had been vaccinated by this method usually 

 showed an increased opsonic index over that of normal animals, fre- 

 quently the number of leucocytes in the abdominal cavity as well as the 

 number of bacteria was very small. The explanation of this phenomenon 

 has already been discussed above. The difficulties in the technique were 

 therefore increased and further experiments were not performed with 

 this method because of the superiority' of the first one described. In the 

 experiments in Series 61 (p. 267) the opsonic index of the animals before 

 vaccination was imfortunately not determined and hence the results are 

 not as valuable for comparison. 



Carrying out experiments in this manner, the details of which are 

 described in Series 61 and 62 (pp. 267 and 268), it has been possible 

 to demonstrate that the blood of an individual or animal vaccinated and 

 immunized against pest usually shows an increased opsonic index. How- 

 ever, that this was not invariably the case may be seen from the tables 

 given in Series 61 and 62. The opsonic power apparently varied some- 

 what according to the virulence of the strain employed, the index usually 

 being higher with the avirulent strain. Xo attempt was made to demon- 



S7 Johns Hopkins Hosp. Bull (1906), 17, 27. 



