THE STREPTOCOCCUS GROUP 313 
Additional suggestion of the Einheit of streptococci has been brought 
forward by Rosenow/ 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 interpretation of experimental mutations of streptococci and 
pneumococci obtained by passage of the organisms through labora- 
tory animals, such as guinea-pigs, must be viewed in the light of 
Holman's- highly important observations of the frequent occurrence 
of streptococci and pneumococci in the tissues, and even the blood of 
guinea-pigs which have not been artificially inoculated with either of 
these organisms. The many variables to be considered in this con- 
nection—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 
by serological and pathological methods, and that these types were 
mutually stable, for long-continued passage through animals failed to 
alter or modify their general cultural and agglutinating properties, 
although the virulence of the respective types of one or another 
animal could be increased or decreased. It is not improbable that 
a thorough study of the streptococcus group may reveal similar sero- 
logical variance and that in the t\'pe now designated Streptococcus 
pyogenes several individual types parallel to those of the pneumococcus 
may be demonstrated. 
The important question for the moment is, do these changes of 
virulence, et cetera, exhibited by the streptococcus influence the diag- 
nostic aspect of the question? Theobald Smith has admirably 
summed up the present status of the subject in the following words: 
"Spontaneous changes in the cultural characters of the streptococcus 
do not proceed rapidly enough, if they go on at all, to interfere with 
1 Loc. cit. 
2 Am. Jour. Med. Sci., 1917, 153, 427. Ibid., Jour. Med. Re.s., 1910, 35, 1.51. 
