THE USE OF CONGO RED IN CULTUEE MEDIA. 17 



CONCLUSIONS. 



It is interesting to observe that none of the organisms tested up to 

 the present time show as strong an absorption of dye from the syn- 

 thetic nitrogen-poor medium as do certain strains of Bacillus tnme- 

 jaciens^ wliile upon beef agar four otlier species exliibit the greatest 

 activity. Practically all stab and streak cultures show more or less 

 absorption along the edge of the broken agar surface, but this seems 

 to be due to the staining of slime where the bacterial growth is oldest 

 and to the staining of dead bacteria killed in transferring. The 

 living bacteria themselves, however, of at least certain strains of 

 such species as Bac'dJus tumefaciens^ B. butyricus, B. prodigiosns, 

 B. lactis, etc., can absorb congo red, which, like the relation of bac- 

 terial strains to gentian violet described by Churchman and Howard,^ 

 would seem to indicate that this phenomenon is associated with some 

 protoplasmic function. Observations upon bacterial cells of Azoto- 

 hacter cliroococcum impregnated with congo red show that upon cell 

 division at least frequently one red and one colorless cell are formed. 



1 Churchman. John W., and Howard, Michael W. The selective action of gentian 

 violet on closely related hacterial strains. .Tovirnal of Experimental Medicine, v. 16, no. 

 G, PI). 8L'2-830. 1012. 



[Cir. 130] 



