CHAPTER XXX. 

 PHAGOCYTOSIS-OPSONINS. 



It has been mentioned that Metchnikoff, in a pubUcation 

 in 1883, attempted to explain immunity on a purely cellular 

 basis. It has been known since Haeckel's first observation 

 in 1858 that certain of the white corpuscles do engulf solid 

 particles that may get into the body, and among them bac- 

 teria. Metchnikoff at first thought that this engulfing and 

 subsequent intracellular digestion of the microorganisms 

 were sufficient to protect the body from infection. The 

 later discoveries (discussed in considering Ehrlich's theory 

 of immunity) of substances present in the blood serum and 

 even in the blood plasma which either destroy the bacteria 

 or neutralize their action have caused Metchnikoff to modify 

 his theory to a great extent. He admitted the presence of 

 these substances, though giving them other names, but 

 ascribed their formation to the phagocytes or to the same 

 organs which form the leukocytes— lymphoid tissue gener- 

 ally, bone-marrow. It is not within the province of this 

 work to attempt to reconcile these theories, but it may be 

 well to point out that Ehrlich's theory is one of chemical 

 substances and that the origin of these substances is not 

 an essential part of the theory, so that the two theories, 

 except in some minor details, are not necessarily mutually 

 exclusive. 



Sir A. E. Wright and Douglas, in 1903, showed that even 

 in those instances where immunity depends on phagocytosis, 

 as it certainly does in many cases, the phagocytes are more 

 or less inactive unless they are aided by chemical substances 

 present in the blood. These substances act on the bacteria 

 not on the leukocytes, and change them in such a way that 

 they are more readily taken up by the phagocytes. Wright 



(279) 



