CHAPTER XVIII 



OPSONINS, LEUCOCYTE EXTRACT, AND AGGRESSINS 

 OPSONINS 



ALTHough- the theories of immunity are, as we have stated, generally 

 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 complement, in the leucocytes, and 

 Metchnikoff attributed to immune serum the quality of stimulating the 

 leucocytes (stimulins) to increased phagocytosis. The serum, accord- 

 ing to Metchnikoff, acted, not directly upon the bacteria, in the nature 

 of bactericidal or lytic substances, but rather upon the leucocytes, pre- 

 paring or arming these for the fray. Denys and Leclef x were the first 

 definitely to oppose this view. These authors, on the basis of ex- 

 periments 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 re- 

 lation of the blood serum to phagocytosis, in a series of careful experi- 

 ments. Using his own modifications of the technique of Leishman, 3 

 he first determined the direct dependence of phagocytosis upon some 

 substance contained in the blood serum. He further proved conclu- 

 sively 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. 



* Wright and Douglas, Proc. Royal Soc. London, Ixxii, 1904. 



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



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