48 VACCINE AND SERUM THERAPY. 



24 leucocytes, have some choice for the 25th one to he examined, 

 which choice would change the result from 1 to 17. Based on 

 this selection the opsonic index could be materially lowered or 

 raised as might be desired. 



In one of the early contributions on the subject of opsonic 

 index, Simon, Lamar, and Bispham recommend that in making 

 the spread of the mixture after incubation, the spreader slide be 

 merely kept in contact with the blood without touching the lower 

 slide, for, "Otherwise it may happen that most of the leucocytes 

 containing organisms, are carried to one end, while only the empty 

 cells are found in the intervening space." In the laboratories 

 of the Johns Hopkins Hospital, Cole, Moss, and Jeans and Sellard 

 have made determinations of phagocytic indices determined in 

 different parts of the slide. It was found that the leucocytes 

 collected near- the edge of the smear contain decidedly more bac- 

 teria than those toward the center of the slide. By dividing a 

 slide into three zones they found that at the end of the smear the 

 leucocytes contain more bacteria than in the first and middle 

 zones. To explain these differences these men assume that the 

 polymorphonuclear leucocytes containing the largest number of 

 bacteria are so increased in size that they are drawn to the end 

 of the slide while the smaller ones drop out earlier. These results 

 indicate that, contrary to Wright's suggestion, one ought not to 

 determine the number of bacteria at the end of the spread. 



Wright's method of the determination of the opsonic index 

 has yielded such marked differences in results that more work on 

 this subject seems justifiable. It must be remembered that the 

 opsonic index is of no value whatever unless carried out with the 

 greatest care and by some one who has had considerable exper- 

 ience. Modifications of Wright's technique have arisen with too 

 much rapidity to make it possible to lay down any definite rule 

 for the determinattion of the opsonic index. However there are 

 only few modifications that have made it possible to get more 

 reliable determinations of Wright's opsonic index. 



