HISTORY OF PNEUMOCOCCUS: 1890-1900 27 



because they passed the strain through eggs. Finally, however, pas- 

 sage through a rabbit restored the degenerated forms to the origi- 

 nal state of the parent strain. Without venturing an explanation, 

 Eyre and Washbourn concluded, "Our experiments are in favor of 

 the theory . . . that the individual cocci or their descendants ac- 

 tually alter in character under varying conditions," or, to use the 

 modern term, dissociate. 



The quest for a potent immune serum was continued by Denys 

 (1897), 312 who met with greater success than did his predecessors. 

 Denys first raised the virulence of pneumococcal cultures by serial 

 passage of infected blood through rabbits, then administered both 

 heated and filtered cultures to normal animals, at first rabbits, 

 then goats, and later horses. After this preliminary treatment, 

 Denys gave a series of injections of unheated cultures, then of the 

 blood of infected rabbits, and finally of living, virulent pneumo- 

 cocci. The serum thus obtained prevented infection, was curative, 

 and neutralized in rabbits the alleged "toxins" of Pneumococcus. 

 The results of controlled experiments convinced Denys that the 

 immune serum so prepared was not bactericidal, but that it 

 contained a substance which stimulated the white corpuscles to 

 phagocytosis, or as he phrased it, Uimmunite du lapin contre le 

 pneumocoque, a sa source dans une modification de son serum; and, 

 L'element immunisant primordial est le serum et le leucocyte par 

 lui-meme n*est rten. 



Pane, 1044 in the same year, not only obtained potent serums from 

 rabbits, cows, and asses, but tested their curative action on human 

 beings. Of twenty-three pneumonia patients treated by intravenous 

 injection, only two died. Pane, incidentally, noted definite aggluti- 

 nation in the test tube and phagocytosis in the blood and therefore 

 was inclined to accept MetchnikofPs theory as affording an expla- 

 nation for the therapeutic action of the serum. 



Mennes 893 fully agreed with Denys' idea that it was the immune 

 serum and not the normal or immune leucocyte which stimulated 

 phagocytosis. He, also, immunized horses, gave the serum intra- 



