CLASSIFICATION OF THE COLON-CLOACAE GROUP 



257 



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The principle of correlation should not be applied indiscrimi- 

 nately to collections of data for systematic purposes. Certain 

 characters and properties have been universally accepted as 

 reliable and appropriate for bacterial differentiation; thus, stain- 

 ing reactions such as the Gram and acid fast stains; spore forma- 

 tion, aerobiosis and anaerobiosis, hardly need to be bolstered 

 up by correlation with other characters to justify their taxo- 

 nomic value. On the other hand the significance of such char- 

 acters as motility, indol production, and fermentation of certain 

 substances, is still debatable. 



Motility is regarded by many as a highly variable property. 

 Perhaps it is in reality a reliable morphological difference. Cer- 

 tainly if it could be shown that this character goes hand in hand 

 f with several others, more reliance and attention should and 

 would be given to motility. The same is true of the indol test. 

 In dealing with gas formation from carbohydrates, alcohols, or 

 poly sac charids, the question naturally arises as to which sub- 

 stance should be given preference for subdivision, or whether 

 all are to be considered of equal taxonomic value. The lack of a 

 criterion for determining the most significant fermentable sub- 

 stances has led to considerable confusion. It has already been 

 pointed out how subdivision on every character studied results 

 in an infinite number of varieties. Where we are dealing with a 

 number of characters each of which is assumed to be of equal 

 taxonomic significance, it would certainly be desirable and 

 advantageous to subdivide on that character which gives the 

 greatest amount of information as to the manner in which the 

 resulting subgroups react with respect to other characters. It 

 is under such circumstances that the principle of correlation of 

 characters may be legitimately, conveniently, and advantage- 



THE JOURNAL OF BACTERIOLOGY, VOL. Ill, NO. 3 



