THE CLASSIFICATION OF BACTERIA . 51 



In the majority of cases the facts regarding certain species 

 "were too few to differentiate between the greater number of the 

 members of these groups. In fact, it is highly probable that 

 many of these so-called species which are members of any one 

 .group are not true species at all, and that at best they are only 

 varieties of some central group organism. 



The conclusion is permanent that probably nine-tenths of the 

 forms of bacteria already described might as well be forgotten 

 or given a respectful burial. This will then leave comparatively 

 few well-defined species to form the nuclei of groups, in one 

 or another of which we shall be able to place all new and suffi- 

 ciently described forms. 



The question of what is a species in bacteriology I shall not 

 undertake to settle. Bacteria are so subject to morphologic, 

 ■cultural, and pathologic variations that one form appears to 

 merge into another, making distinctions often difficult ; and yet 

 a typical form — an ideal species — may exist. 



Bacillus coli and Bacillus typhosus may present to the mind 

 certain characters which we commonly attribute to these two 

 types. These characters determine the species. Variation from 

 these characters may establish varieties of one or the other ad 

 libitum, forming a chain of types or races connecting the two 

 ideal species. Nevertheless, we retain in mind the typical B. 

 coli and the typical B. typhosus as distinct identities. 



That typical forms or species of bacteria do exist no one can 

 deny. These typical forms furthermore present certain definite 

 morphologic, biologic, cultural, and perhaps pathogenic char- 

 acters which establish the types, independent of minor varia- 

 tions. 



The most marked of these types we select to become the 

 centres of groups, around which -are gathered all related species 

 or varieties. The division of the bacteria into groups, so far 

 as said grouping was possible, is outlined in the following 

 tables : — 



