326 INFECTION AND RESISTANCE 



virulence by Deutsch and Feistmantel 65 and by Bail 66 in his so 

 called "aggressins." The latter are supposed to be secreted bacterial 

 substances by means of which the leukocytes are held at bay. The 

 properties we are, at present, considering are probably in no way 

 antichemotactic, but oppose purely the actual ingestion by the 

 leukocyte, nor do they seem to depend upon the secretion of sub- 

 stances which injure the leukocytes. For, in the first place, a 

 profuse accumulation of leukocytes may follow the injection of 

 virulent micro-organisms, and Denys (quoting from Gruber) has seen 

 active phagocytosis of virulent pneumococci, but none of virulent 

 streptococci when antipneumococcus serum was injected with the 

 mixture. 



Rosenow 67 has carried out a thorough investigation dealing with 

 these relations in pneumococcus infection. Seventy-five strains of 

 this organism were all found non-phagocytable when first isolated 

 and the resistant condition was associated with virulence for rabbits 

 and guinea pigs. It was found, moreover, that the resistance to 

 phagocytosis was dependent upon the inability to absorb opsonin. 

 For, while phagocytable non-virulent pneumococci absorbed specific 

 opsonin from serum, the virulent ones failed to do this in proportion 

 to the degree of their virulence. Furthermore, extraction of the 

 bodies of the virulent organisms in lSTaCl solution yielded a substance 

 which inhibited the action of pneumococcus opsonin a true anti- 

 opsonin which he speaks of as "virulin." This discovery, if con- 

 firmed, would supply us with a very simple explanation for some 

 phases of the problem of virulence. It is, indeed, likely that the 

 antiopsonic property is closely bound up with chemical and struc- 

 tural changes which take place in the bacterial cell as it adapts itself 

 to the parasitic conditions. This is plain from the fact that pneumo- 

 cocci and some other bacteria will rapidly lose their virulence when 

 cultivated on artificial media devoid of animal serum, will retain it 

 longer if grown on some serum media, and will rapidly regain it if 

 passed through animals. The formation of a capsule is unquestion- 

 ably a morphological evidence of such a change. Habitually capsu- 

 lated bacteria, like the Friedlander bacillus, and Streptococcus muco- 

 sus, are of fairly constant virulence, while in other micro-organisms 

 like the pneumococci, anthrax bacillus, plague bacillus, and certain 

 other streptococci, the formation of a capsule goes hand in hand with 

 an increase of virulence. By the aid of this morphological earmark 

 of virulence, moreover, Gruber and Futaki have obtained further 



65 Deutsch and Feistmantel. Quoted from Sauerbeck. Lubarsch und 

 Ostertag, Vol. 2, 1906. 



66 Bail. Arch. f. Hyg., Vol. 52, 1905. 



67 Rosenow. Jour. Inf. Dis., Vol. 4, 1907. 



