The Washed Leukocytes 317 



always followed by a temporary diminution (negative phase) 

 of the opsonic index, soon followed, if the dose be not too 

 large, by a marked increase (positive phase). It is sup- 

 posed, upon theoretic grounds, and proved by practical 

 experience, that the increase of phagocytic activity brings 

 about improvement. The care of the operator should be 

 to avoid giving so large a dose of the vaccine that the nega- 

 tive phase will be so long continued that harm instead of good 

 may be achieved. 



Although Wright is said to cling to the study of the opsonic 

 index as a guide to bacterio-vaccination and the resulting 

 degree of immunity, the greater number of workers have 

 abandoned it upon grounds which the writer long ago ex- 

 pressed " that the estimation of the value of bacterio- 

 vaccination by means of the opsonic index was a very com- 

 plicated way of finding out very little." 



