ON SPECIFIC THERAPEUTICS. 39 



means excludes phagocytosis ; destruction of 

 the bacteria outside the cells and their assimi- 

 lation by the phagocytes are processes which 

 may take place alongside each other, and, by 

 their simultaneous action, increase the protec- 

 tive power. A special proof of the importance 

 of the study of haptines appears to me to be the 

 fact that as the opsonin theory, which we owe 

 to Sir Almroth Wright, has made more evident, 

 specific haptine reactions form the basis also of 

 phagocytosis, which Metchnikoff has studied in 

 so masterly a manner. The opsonins and cyto- 

 tropic substances render the bacteria liable to 

 attack by the phagocytes, and here we have a 

 field in which humoral and cellular processes 

 meet. One cannot, however, say that the 

 possible causes of immunity are confined to 

 haptine action and phagocytosis. Perhaps the 

 atreptic view, by which differences of degree in 

 avidity on the one side or on the other are 

 presumed, is correct in many cases in which 

 other influences are at work. This view of the 

 case I shall treat more fully when I come to 

 speak of carcinoma. 



The immunity of an animal is, therefore, ex- 

 plained as being due to the great energy of the 

 cells of its body, which are able to appropriate 



