PHAGOCYTOSIS 



267 



Hence the opsonic school of immunity has formed a theory 

 which may be enunciated as follows : The immunity to certain 

 organisms (not to all) depends on phagocytosis, and this can only 

 take place in virtue of the preparation of the organism by the 

 action of opsonin. Where this substance is present in normal 

 amount the person is sufficiently immune to resist ordinary 

 infections; but if for any reason the amount is lowered or the 



2 



1-8 

 1-8 

 1-7 

 1-6 

 1-5 

 14 

 1-3 

 1-2 

 l-l 

 1-0 

 9 

 8 

 7 

 6 

 5 

 4 

 3 

 2 



FIG. 61. OPSONIC INDEX IN DIPHTHERIA. (Tunnicliffe.) 



infection very virulent, phagocytosis cannot occur, and the disease 

 progresses. There is then a new formation of opsonin, just as 

 there is of other antibodies, and this goes on until there is 

 sufficient to sensitize all the bacteria and render them amenable to 

 phagocytosis, when recovery occurs. When this does not take 

 place the patient's phagocytes cannot ingest the bacteria, and the 

 disease progresses. 



There is one assumption that will require critical consideration 

 subsequently, and that is that opsonin is an antibody. 



The behaviour of the index in chronic infections is different, 



