IMMUNITY IN PNEUMOCOCCAL INFECTIONS 23 



very little change in the opsonic index. The time given for the inter- 

 action of the fluids, bacteria and leucocytes, did not allow either the 

 cocci to be thoroughly opsonised or the leucocytes to take up the cocci 

 that were opsonised. If the interaction is allowed to go on for 45 

 minutes, the result is somewhat different : — 



Cocci per 

 leucocyte. 

 Normal serum 3 pts. 16-7 



Normal serum 2 parts + Normal saline i pt. - - 117 



n I part 4- II 2 pts. - - 5*9 



II J part + II 2J pts. - 3*4 



(Normal serum : Saline = i : 8) 3 parts - - - 1-9 



( n M =1 : 10) 3 parts - - i'8 



The numbers in this latter experiment fall almost exactly proportional 

 to the dilution. 



From this and the preceding experiment the conclusion to be drawn 

 is that the most accurate means of determining the opsonic content and 

 opsonic index of any serum is to allow either the serum, leucocytes and 

 bacterial emulsion, to interact for at least 30 to 45 minutes, or to dilute 

 the serum one part in 3 parts with normal saline, if the period of 

 interaction allowed is to be 15 minutes. 



Effect of dilution with Na CI. solutions stronger than 0'85 per cent. 



Cocci per 

 leucocyte. 



Normal serum 3 volumes - - - - - - 10*5 



Normal serum i vol. + '85 °l^ Na CI., 2 vols. - - - 4*3 



M +I'0% II - - - 2-0 



+ 1-5 7o " - - - 1*7 



u + 2 % II - - - 1-6 



+ 5 7o " - - - 1-3 



(These were incubated with leucocytes and coccal emulsion for 30 

 minutes.) Increasing the concentration in salt seems to diminish the 

 amount of opsonising power of the serum. 



It is affirmed by Buchner that the destruction of alexine on heating 

 to 55° C. can be paralysed by adding salt. Whether the same was true 

 of opsonin was tested. Normal serum was diluted in the proportion of 



(387) A A I 



