CLASSIFICATION OF STREPTOCOCCI 413 



Tunnicliff. 39 She has given particular attention to absorption tests, 

 and has found, in agreement with Bliss, that the hemolytic strep- 

 tococci from scarlet fever form a distinct group, these organisms 

 removing opsonins and agglutinins for these cocci, whereas, ery- 

 sipelas cocci have no such effect. With scarlet fever streptococci 

 in a sheep, Tunnicliff produced a serum which agglutinated hemoly- 

 tic streptococci in dilutions of 1 to 2000, and opsonized them in 

 dilutions of 1 to 360. She found that this serum protected mice 

 against the hemolytic streptococci isolated from scarlet fever pa- 

 tients, but not from erysipelas, mastoiditis and influenza. This pro- 

 tective powder was rapidly lost by the sheep serum, but was restored 

 by the addition of normal sheep serum. Her further work indicates 

 that, like the scarlet fever cocci, the erysipelas cocci form a distinct 

 group, also. 



As we shall see, the difficulty with these investigations has largely 

 been technical in that the spontaneous agglutination of the hemolytic 

 streptococci makes it very difficult to carry out reliable agglutination 

 work. These difficulties will be alluded to in connection with ag- 

 glutination. 



Virulence and Pathogenicity. Different races of pyo genie strep- 

 tococci show considerable variations in virulence, and there are few 

 organisms, pathogenic both for animals and man, which show com- 

 parable fluctuations in virulence. The character or severity of the 

 lesion in man gives little evidence as to the virulence of the organism 

 for animals. Such differences are, to a certain extent, dependent 

 upon inherent individual characteristics, but are rather more likely 

 to be the consequences of previous environment or habitat. Pro- 

 longed cultivation upon artificial media usually results in the reduc- 

 tion of the virulence of a streptococcus, while an originally low or 

 reduced virulence may often be much enhanced by repeated passage 

 of the streptococci through animals. It is noteworthy, however, 

 that while the passage of a streptococcus through rabbits will usually 

 enhance its virulence for susceptible animals in general, repeated 

 passages through mice may increase the virulence for these animals 

 only, even occasionally depressing the virulence for rabbits. 



Among the domestic animals, those most susceptible to experi- 

 mental streptococcus infection are white mice and rabbits. Guinea- 

 pigs and rats are less easily infected, and the larger domestic animals, 



30 Tunnicliff, Jour, of the A. M. A., 75, 1920, 1339. 



