62 BACTERIOLOGY FOR NURSES 



there entering into a struggle with the microorgan- 

 isms. 7 ' (Metchnikoff, 1905.) 



Opsonins. An immense amount of research fol- 

 lowed Metchnikoff' s discoveries, one of the great 

 problems being to find the reason why the leucocytes 

 do not always attack the bacteria and prevent infec- 

 tion. Among the investigators was Sir A. E. Wright 

 of England, who, with others, discovered that the 

 blood-serum contains substances which are necessary 

 to prepare the bacteria for the leucocytes; these 

 substances he called opsonins. Opsonins are in the 

 blood of normal animals, but are greatly increased 

 by immunization and differ for different bacteria. 

 The process whereby the opsonins change the bac- 

 teria and render them liable to phagocytosis is not 

 perfectly understood. 



The opsonic index is the mode of expressing the 

 relative amount of opsonins contained in the blood- 

 serum in comparison to the normal. 



The technique of this work is extremely compli- 

 cated and delicate. 



The opsonic method of treatment aims to main- 

 tain the opsonic index at a high level, which insures 

 the phagocytic power of the blood. 



" Wright and Douglas and their followers have found it 

 possible to artificially increase the production of opsonins 



