DILUTIONS OF SERUM. 41 



Bolduan has reported determinations of the opsonic index 

 of normal individuals and finds that as far as the bacillus of tuber- 

 culosis, staphylococci and streptococci are concerned, there is 

 marked variation not only in different individuals but also from 

 day to day. 



Moss has found opsonic indices for staphylococci to vary 

 from 0.18 to 0.56 in normal rabbits. 



The same serum has also been tested a number of times 

 with the same leucocytes and bacterial emulsion. Bolduan re- 

 ports opsonic index determinations for a single serum which 

 vary from 1 . 05 to 1 . 46. The writer has reported determinations 

 made by taking five specimens of blood from the five fingers 

 of the same hand of a healthy adult. The leucocytes used for 

 the determination were washed twice in 1.5 per cent potassium 

 citrate in normal salt solution. The phagocytic indices for 

 Mic. pyogenes aureus are shown in the table: 



1st 100 leukocytes 2d 100 leukocytes Phagocytic 



counted. counted. index. 



Specimen 1 166 196 1.810 



2 176 183 1.79.') 



3 198 199 1.985 



4 185 175 1.800 



5 230 190 2.100 



If the indices for each specimen of blood be compared with 

 all the others, the opsonic index as determined by counting the 

 number of cocci in two hundred cells will be found to vary from 

 0.85 to 1.22. 



It thus seems evident that if normal serum varies as much 

 as has been found, the variations from the normal, unless marked, 

 can indicate but little. The most that would seem warranted 

 is to determine whether a serum is "high" or "low" in opsonic 

 content, as the case may be. 



Dilutions of Serum. 



Wright has usually used undiluted serum in the determina- 

 tion of the opsonic index. Simon, Lamar and Bispham have 

 shown that by the dilution of some sera there often is a rapid 

 exhaustion of phagocytic power of the leucocytes. They have 

 observed that undiluted pig's serum manifests a most intense 

 opsonizmg effect on staphylococci but that this action diminishes 

 markedly upon dilution of the serum. Human serum, on the 

 other hand, though not having as marked an initial opsonizing 



