PHAGOCYTOSIS AND ADAPTATION 53 



have no effect upon the Spirillum metchnikovi which sets up 

 an intense diarrhoea in fowls, or with other non-pathogenic 

 spirilla obtained from water. Only rarely in animals immunized 

 against other species of bacteria do we note the existence of a 

 group reaction — a certain amount of digestion exercised by the 

 concentrated serum upon allied forms, though when the serum 

 is diluted the reaction becomes narrowly specific. For present 

 purposes I need not enter into the evidence afforded that for 

 this bacteriolytic action the coexistence of two bodies is essential, 

 namely the complement present in the body fluids of the normal 

 (and also of the immunized) animal and the immune body, or 

 amboceptor elaborated by the treated animal in the process of 

 immunization, nor into Metchnikofl and Bordet's demonstra- 

 tion of the presence of these two factors. All that is necessary 

 is to call attention to one of the commonplaces of bacteriology 

 that immunization is adaptation, and that while in some cases it 

 is of the nature of exaltation of properties already possessed, 

 in others it is clearly the acquirement of a new property. 



Phagocytosis 



I need scarcely say that by a different means of approach, 

 namely through the intimate study of cell function, the admirable 

 studies of Metchnikoff, extending from the early 'eighties of 

 the last until the beginning of this century, 1 teach the same 

 lesson. Those studies brought together in his two works upon 

 the Comparative Pathology of Inflammation and upon Immunity 2 

 demonstrated in a very beautiful manner that in the repair of 

 injury, the destruction of microbes and the production of im- 

 munity, the leucocytes play a foremost part, and what is more, 

 that the development of immunity is intimately associated with 

 the accustomance, education, or adaptation of certain orders of 

 leucocytes and other cells. Cells which at first are not attracted 

 towards microbic foci eventually become actively attracted, cells 

 which at first show little or no signs of incepting bacteria eventu- 



1 His later studies upon senility and the prolongation of life, while highly 

 suggestive, were not, in my opinion, of the same high scientific value. 



a La Pathologie comparee de V inflammation, Paris, Masson, 1892. English 

 translation by Starling, 1893. Ulmmunite dans Us maladies infectieuses, 

 Paris, Masson, 1901. English translation by Binnie, Cambridge University 

 Press, 1905. 



