40 VACCINE AND SERUM THERAPY. 



the opsonic index of a normal individual will vary from 0.8 to 

 1.2. To obtain the true amount of opsonin in normal serum, he 

 pools equal quantities of sera from several normal individuals. 

 However, after it has been established that a healthy individual 

 has an opsonic index of 1.0, as determined by estimation with 

 pooled normal sera, he uses serum from this individual as a normal 

 serum. Wright's own determinations, from which he concedes 

 that there are variations in the amount of opsonin present in 

 the blood of healthy .individuals, discredit the accuracy either 

 of the method of determining the opsonic index or the value of 

 determining the same. If the opsonic indices of two normal in- 

 dividuals is . 8 and 1 . 2 respectively on the same day as deter- 

 mined by co parison with pooled normal serum, then as com- 

 pared to each other their opsonic indices vary from 0.66 to 1.5 

 respectively. It is thus evident that from Wright's concession 

 the index of a normal individual may vary from . 66 to 1.5 

 when one serum is used as a control for the other. 



Indices for normal serum as actually determined will not 

 even vary within these limits. The writer sometime ago reported 

 results on a series of ten specimens of blood from ten healthy 

 adults, studied to determine the differences in opsonic power in 

 healthy individuals. The leucocytes were washed twice with 

 0.85 salt solution. The number of staphylococci taken up by 

 100 polynuclear leucocytes was counted in two preparations, sepa- 

 rately incubated. The phagocytic indices as determined by two 

 workers A and B are as follows: 



Source. A B 



N ... 9.48 7.63 



J 9.16 5.20 



B 8.75 6.80 



McL 7.27 4.37 



Z 6.63 5.12 



C 6.60 5.37 



S 5.89 4.82 



5.84 4.57 



H 5.49 6.03 



Ns 4.91 4.37 



The great error introduced by this method becomes evident 

 upon the determination of the opsonic indices when each serum 

 is used for comparison with all of the others. In the series A, 

 the normal opsonic index varies from 0. 52 to 1 . 93, while in series 

 B it varies from 0.57 to 1.75. Moreover, the indices obtained 

 by the two workers A and B vary considerably for the same sera. 



