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IVAN C. HALL 



perhaps nutrient conditions, as Burke (1919) has mentioned. 

 On standing longer the blue band thickens, and it is suggested 

 that the distance from the surface at which anaerobic growth 

 commences is determined partly by the rapidity of multiphcation 

 permitted by the nutritional conditions of the culture. 



Deep tubes of agar, in which recoloration of decolorized meth- 

 ylene blue is occurring, present the phenomenon of rhythmic 

 banding, i.e., Liesegang's rings. This subject has been studied 

 recently by Holmes (1918) in other cases, but no one, so far as 

 I am aware, has investigated the phenomenon in the case of 

 methylene blue, for which no really satisfactory explanation is 

 available. 



TABLE 4 

 Depth of returning blue band in decolorized methylene blue agar of varying densities 



Other methods of deep culture involving soUd or semi-solid 

 media present phenomena analogous to those observed with 

 deep agar tubes. Thus gelatin and deep brain media with 

 methylene blue remain decolorized in the depths for several 

 days after heating but the immediate coloration in the upper- 

 most layer gradually extends downward as oxygen and carbon 

 dioxide are absorbed. Corresponding to the usual failure of 

 cultural tests with unprotected Uquid media, alkahne glucose 

 solutions of methylene blue regain their color on exposure to 



