78 UNIVERSITY OF WISCONSIN STUDIES 



classification. The hopelessness of establishing a stable classi- 

 fication by using only the fermentations of various substances 

 is shown by the large number of proposed schemes, some of 

 which permit over one hundred possible varieties. The one 

 which has b?en most generally followed was proposed by 

 MacConkey and is merely the possible combinations of the 

 plus and minus signs under two test substances. The four 

 species permitted by this arrangement may, by applying 

 similar methods, be further divided into varieties, limited 

 only by the number of test substances used. A classification 

 of this kind may be convenient in that it adapts itself readily 

 to a workable key but there is no evidence to show that it has 

 any relation to the evolution of the group or that it serves 

 in any way to indicate the origin of the culture. 



It should be possible to discover some combination of char- 

 acters which separates the group into natural species. Since 

 the evolution of a bacterial species is largely a question of 

 environment, the species so established should be coincident 

 with more or less well-defined habitats. For taxonomic pur- 

 poses it may safely be assumed that the nature of the fer- 

 mentation is of more significance than the particular material 

 fermented. 



THE CHARACTERS STUDIED 



The characters of a group of bacteria can be properly 

 established only by studying a considerable number of cul- 

 tures. The value of this method of stud}' has been so com- 

 pletely demonstrated by some of the recent work on systematic 

 bacteriology, particularly by the work of the Winslows on the 

 Coccaceae, that its use should need no further justification. 

 In attacking this problem we have so far as possible used 

 exact chemical methods in determining the reactions produced 

 by the bacteria in various culture media. This has limited 

 the number of cultures which could be studied but has per- 

 mitted distinctions on the basis of quantitative measurements 

 which have been of the greatest value. The details of the , 

 methods followed have been given in the papers cited and 

 for the sake of brevity will not be repeated here. The cul- 



