COMPARATIVE STUDY OF THE COCCI 57 



systematically recorded. The only significant differ- 

 ences between various non-liquefying colonies lie in the 

 amount of surface growth and the color, both of which 

 characters are more easily studied on the agar streak. 

 The nature of the surface growth, like that of the 

 gelatin plate colony, does not appear in this group to 

 offer any character of diagnostic value, and all the cocci 

 grow fairly well in the stab. Among the liquefying 

 forms we have not found the shape of the liquefaction 

 of sufficient constancy to be recorded. Whipple (1902) 

 has shown the uncertainty of this character — almost 

 every possible type appearing in media made with 

 slightly different commercial gelatins. The Committee 

 on Standard Methods (1905) has also omitted this 

 property. 



The amount of liquefaction of gelatin was therefore 

 the only character recorded in the gelatin tube. The 

 method by which this was measured will be described 

 under " Biochemical Reactions." 



Agar plates. The same reasons which led us to omit 

 the gelatin plate militate against the use of the agar 

 plate as a diagnostic test. Constant differences between 

 colonies are slight and depend on a few fundamental 

 properties which may be more easily observed on other 

 media, notably on the agar streak. 



Agar tubes. The general conclusion from what has 

 been said in this discussion of cultural characteristics 

 is that in the cocci a single medium is sufficient for their 



