312 INFECTION AND RESISTANCE 



the nature of streptococcus immunity in rabbits. It established, first 

 of all, the paramount importance of phagocytosis in the resistance 

 of animals against these bacteria, and made clear that the destruction 

 of bacteria was carried out equally as well by the leukocytes of nor- 

 mal as by those of immune animals, but was powerfully enhanced 

 when either normal or "immune" leukocytes were combined with 

 immune serum. Their work, therefore, indicated again that the in- 

 creased phagocytosis of virulent bacteria, taking place in immune 

 animals, depended clearly upon alterations in the functions of the 

 serum rather than in those of the cells, and they suggested that 

 the influence of this serum was not necessarily one of leukocyte 

 stimulation, but might rather consist in action upon the bacteria, 

 rendering them less resistant to phagocytosis. They say in sub- 

 stance: "A notre avis, on pourrait tout aussi bien admettre que la 

 substance vaccinante ou antitoxique agit, non pas sur le leukocyte, 

 mais sur un poison renferme dans le corps du microbe ou dissous 

 dans le milieu, et qui preserve le micro-organisme centre les at- 

 teintes du leukocyte." 4 



In this statement we have, in brief, the distinct formulation of 

 our present view of the "opsonins." 5 



Observations with pneumococci and streptococci carried out 

 after this by Marchand 6 and by Mennes, 7 whose investigations we 

 cannot discuss in detail, beside confirming most of the observations 

 of Denys and Leclef, brought out especially the relation of the 

 virulence of micro-organisms to phagocytosis, showing that very 

 virulent strains were taken up to a slight degree only in the presence 

 of normal serum, but were subject to active phagocytosis when im- 

 mune serum was employed. This, too, seemed to point primarily to 

 the fact that the serum influenced rather the bacteria than the 

 phagocytes, although no convincing proof is brought for this in their 

 publications. Though much that had bearing indirectly on thia 

 problem was written during the following years, no definite progress 

 was made beyond the results of Denys and his pupils until 1902, 



4 In our opinion one can just as well believe that the vaccinating or anti- 

 toxic substance acts not upon the leukocyte but upon a poison inclosed within 

 the body of the bacteria or dissolved in the medium, which preserves the 

 micro-organism against the attacks of the leukocyte. 



5 Denys formulated this view with still greater clearness and positiveness 

 at the Congress of Hygiene held at Brussels in 1903. We take our citation 

 from the discussion on opsonins by Gruber (3d meeting Freie Vereinigung f. 

 Mikrobiol., Vienna, 1909, Centralbl f. Bakt., I Ref., Vol. 44, Suppl. p. 3). 

 Following is Denys' statement: 1. The phagocytosis in immune sera is de- 

 pendent upon substances which are precipitated with the euglobulins. 

 2. These substances cause phagocytosis by inciting a physical alteration of 

 the micro-organisms. 3. These substances are specific. 



6 Marchand. Arch, de Med. Exp., 1898. 



7 Mennes. Zeitschr. f. Hyg., Vol. 25. 



