CHAPTER XVIII 



OPSON1NS AND VACCINE THERAPY. LEUCOCYTIC SUBSTANCES. 

 NON-SPECIFIC PROTEIN THERAPY. VIRULENCE 



OPSONINS 



ALTHOUGH the theories of immunity are, as we have stated, gen- 

 erally classified as the humoral and the cellular or phagocytic theories, 

 the separation has never, even in the minds of the warmest partisans, 

 been an absolute one. Thus, Buchner and his successors looked for 

 the origin, first, of alexin, then of antibody, in the leucocytes, and 

 Metchnikoff attributed to immune serum the quality of stimulating 

 the leucocytes (stimulins) to increased phagocytosis. The serum, 

 according to Metchnikoff, acted, not directly upon the bacteria, in the 

 nature of bactericidal or lytic substances, but rather upon the leuco- 

 cytes, preparing or arming these for the fray. Denys and Leclef 1 

 were the first definitely to oppose this view. These authors, 'on the 

 basis of experiments done upon streptococcus immunity in rabbits, 

 came to the conclusion that the serum aided phagocytosis rather by its 

 action upon the bacteria than by its influence upon the leucocytes. 



Wright 2 in 1903 and 1904 undertook a systematic study of the 

 relation of the blood serum to phagocytosis, in a series of careful 

 experiments. Using his own modifications of the technique of Leish- 

 man, 3 he first determined the direct dependence of phagocytosis upon 

 some substance contained in the blood serum. He further proved 

 conclusively that this serum component acts upon the bacteria directly 

 and not upon the leucocytes, is bound by the bacteria, and renders them 

 subject to phagocytosis. The presence of these substances in sera, 

 furthermore, which appear entirely free from bactericidal or lytic 

 bodies, and the thermolabile character of the substances (60 for ten 

 or fifteen minutes destroys them) seemed to exclude their identity with 

 the immune bodies of other authors. 



1 Denys et Leclef, La cellule, xi, 1895. 



2 Wright and Douglas, Proe. Royal Soc. London, Ixxii, 1904. 

 'Leishman, Brit. Med. Jour., i, 1902. 



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