CRITICISM OF CALCULATION OF OPSONIC INDEX. 45 



off after the first centrifugalization while others have attempted 

 to remove the serum of the blood and the citrate or oxalate 

 solution by several washings with normal salt solution. 



To the source of the leucocytes Wright attaches little impor- 

 tance, while most other investigators have aimed to obtain leuco- 

 cytes from the blood of apparently healthy individuals. The 

 work of Peterson and Hiss and Zinsser indicates that the leuco- 

 cytes contain substances that are of importance in immunity 

 and that these substances vary in the leucocytes of normal and 

 immunized animals. For this and other reasons it seems advis- 

 able in all cases to obtain the leucocytes from the blood of normal 

 individuals. 



Walker draws the blood from which the leucocytes are to 

 be obtained into citrate solution heated to 37 C. The leuco- 

 cytic cream is kept at this temperature up to the time of mix- 

 ture with serum and bacterial emulsion. He believes this to be 

 of great importance. In experiments performed by the writer 

 and others, this has not been found to be of especial value in the 

 production of uniform phagocytosis, nor do Walker's tables 

 show a marked uniformity, for the number of bacteria per 

 leucocyte vary from 1 to 1 7 in twenty-five leucocytes examined 

 on the same slide. 



CALCULATION AND DETERMINATION OF THE 

 OPSONIC INDEX. 



According to Wright's method the opsonic index is deter- 

 mined and calculated by dividing the degree of phagocytosis ob- 

 tained with patient's serum by that obtained with serum from a 

 normal individual. 



Simon has proposed an entirely different method for the 

 calculation of the opsonic index. He had observed that with 

 many species of bacteria, due to lysis and fragmentation, great 

 difficulty is experienced in determining the phagocytic index and 

 that the strength of emulsion greatly changes the amount of 

 phagocytosis. To remedy this, Simon first proposed that the 

 percentage of phagocytic cells be determined by counting 50 cells 

 taken in sequence. Later Simon compared the percentage of 

 phagocyting leucocytes with patient's serum to the percentage 

 of phagocyting cells with pooled normal serum. The value ob- 



