62 BACTERIOLOGY FOB NURSES 



there entering into a struggle with the microorgan- 

 isms." (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 o^oi^ns. Opsonins are m the_ 

 blnoH nf normal animajf^^ hnt, are greatly increased 

 by immunization and differ for different bacteria. 

 The process whereby the jjpsnnjns change the haii^ 

 teriaand render them hable to phagocy tosis, is not 

 perfectly understood. 



The o'psonic 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 



