1912.] 



On the Variability of Streptococci. 



407 



It appears, therefore, that even in these selected cases the types 

 •differentiated by the tests lack something in definition and distinction. 



Table IV. — Showing the Eeactions indicated by Gordon for certain 

 " Approved Types " of Streptococci expressed in a Table. 



























Milk. 































































Streptococci 





Clot. 



Neutral red 



g 

 1 



Lactose. 



1 





Saliciu. 



Mannite. 



Number of 

 forms all 

 this serie 

 actions. 



Salivarius 









+ 





















2 



Pyogenes 













+ 



+ 











+ 

 





 + 



8 



Fsecalis 









+ 



+ 











+ 





1 



Possible Meaning of the Reactions. 



Hitherto, attention has been directed to the lack of constancy of the tests, 

 and with that object examples have chiefly been used in illustration which 

 showed a noteworthy degree of variability. But it is not to be supposed on 

 that account that every streptococcus will at any moment necessarily exhibit 

 variation. Within the limits of my own experiments, it has not always 

 been possible to produce variation in particular streptococci even after 

 several months of manipulation, though at another period, or under different 

 conditions, the same streptococci frequently exhibited considerable variability. 

 Again, streptococci which have given a series of variations over a consider- 

 able period may later on preserve an appearance of constancy even after the 

 lapse of a long interval of time, as in the case of streptococcus G- in agar 

 culture in June, 1910, and January, 1912. But no streptococcus yet 

 examined in these experiments has preserved unchanged the whole of its 

 reactions throughout the whole period of observation. 



We do not at present sufficiently understand the conditions governing 

 streptococcal variation or the conditions of temporary constancy, but much 

 of the evidence seems to point in the direction of a distinct environmental 

 influence. 



The question is not an easy one to investigate, owing to the difficulty 

 of supplying absolutely constant conditions of environment even in the 

 laboratory cultivation of streptococci. But it is at least possible that 

 particular nutritive and other conditions in the environment favour the 



