18 



MODERN BIOLOGIC THERAPEUSIS 



further proved that this substance acts directly 

 upon bacteria, is bound by the bacteria, and 

 renders them more easily ingested by the leu- 

 kocytes. To this substance they gave the name 



Marcello Malpighi (1628-94). 



' ' opsonin. ' ' Thus, the gap between the original 

 cellular theory of immunity which ascribed pro- 

 tection and cure to phagocytosis, and the hu- 

 moral theory which ascribed the chief role to 



