1912.] Method for Opsonic Index Estimations. 



143 



Table B. — Opsonic Index. (New Method.) 

 Repeated estimation of the opsonin to Staphylococcus aureus in normal serum, 



using leucocytes only and the opsonic " mill." 

 The series number indicates a set of four or six observations made at a sitting 

 with the same set of materials. 



Series 



Opsonic 

 count, 



50 leuco- 

 cytes. 



Error 

 average. 



Error 

 average. 



Mean 

 value. 



Blanks, 



50 leuco- 

 cytes. 



Worst 

 error 



average 







"Worst 



av2r e 



avera n e. 









per cent. 



per cent. 







per cent. 







per cent. 



1. Very thin bacterial 



61 



16 



— 



i r 



27 



— 



16 



emulsion 











I I 

















[ 72i 



21 

 19 

 20 







79 

 67 



6 





i i 









84 





15 



J ^ 



14 



15 





2. Thin bacterial 



117 





13 



1 f 



13 



13 







103 







| 1 



13 









114 



J 



11 





12 









87 



15 





j-103-j 



11 





15 





91 



11 





1 i 



10 









108 







J L 



18 







3. Hedium bacterial 



130 



6 







6 





6 



emulsion 



147 





5 





9 



5 







135 



2 





H 



11 









144 





3 





8 







4. Thick bacterial 



160 



10 







4 





10 





195 





9 





3 









197 





10 



H 



6 







© 



163 











10 





Total 



74 



84 





Average error above or below the mean value = 158/20 = 7 '9 per cent. 



"Worst error above the mean value = 15 „ 



"Worst error below the mean value = 16 



The results recorded in this table (B) show a marked reduction of the 

 average and maximum error from the mean value, and this had occurred in 

 spite of a fairly wide variation in the strength of the bacterial emulsion 

 used. Believing that still higher accuracy might be obtained I undertook 

 a further series of tests, matching the emulsion used in Experiment 3, 

 Table B (which had been fixed by heat), as a standard. I also decided to 

 count 100 leucocytes, 50 from each of the two films made from the 

 mixture. 



