THE STREPTOCOCCUS GROUP 281 



the site of the focal infection; with a greater loss of virulence, the 

 joints. It must be remembered in this connection that the virulence 

 of a streptococcus for man does not necessarily determine the virulence 

 for animals. 



It is possible to raise the virulence of streptococci very materially 

 by artificially creating portals of entry and of escape which are not 

 usually available to the streptococcus. This is accomplished by 

 passage through experimental animals. By passage it is possible 

 to reproduce with considerable accuracy the various reactions men- 

 tioned above, depending upon the virulence of the organism, the 

 tissue into which the injection is made, and the number of organisms 

 introduced. It is also important to remember than an increase in 

 virulence for one animal, attained by frequent passages, frequently 

 results in a loss, partial or complete, of the virulence of the organism 

 for another animal. Too little is known of the mechanism of virulence, 

 however, to place a final interpretation upon the biological signifi- 

 cance of changes in pathogenic powers. 



Additional evidence of the Einheit of streptococci has been brought 

 forward by Rosenow, 1 who states that he has changed streptococci 

 to pneumococci and back again by special methods of culture and 

 animal inoculation. Two possibilities present themselves to explain 

 this phenomenon, if Rosenow's claims are substantiated. First, the 

 streptococcus-pneumococcus complex is a single organism which 

 exhibits nodes of relative cultural stability (assuming that present- 

 day methods for the recognition of bacterial types are fundamentally 

 sound), and the organism may pass from one node to another under 

 the stress of environmental stimuli. The second possibility is that 

 the streptococcus and pneumococcus are in reality distinct biological 

 entities and that an actual discontinuous mutation has occurred. 

 The many variables to be considered in this connection variations 

 in virulence, adaptability to various hosts, and changes in appearance 

 in different media, all of which may change independently of or parallel 

 to each other complicate the problem to a considerable degree; 

 final judgment must await the establishment of authoritative standards 

 for bacterial diagnosis of unquestioned fundamental stability. 



Neufeld, and Cole and his associates have presented a new aspect 

 of the problem. They found that the older conception of the unity 

 of the pneumococcus type was untenable. They found there were 

 four distinct types of pneumococcus which were recognizable both 



1 Loc. cit. 



