MORPHOLOGY, STAINING PEOPERTIES, ETC. 9 



Differentiation and Identification of Bacteria. 



These very low forms of plant life show a marked susceptibility to 

 environmental conditions and those desirous of speculating on prol)- 

 lems in evolution may find here food for thought and experimenta- 

 tion. On account of this susceptibility, various cultures which belong 

 to the same species may possess slight variations in some one or more 

 specific characters. Consequently one can not say that a species must 

 possess certain definite characters and no others. It is convenient, 

 then, to think of a species as more or less of a group of individuals 

 whose characters approximate each other very closely. 



. In this paper are described a number of species each of which, in 

 fact, represents a group, the individual cultures of which approxi- 

 mate each other so closely in character that the differences may be 

 easily attributed to environmental conditions which are more or less 

 recent. 



Concerning the identification of species, the conditions have been 

 well summed up by Chester. He saj^s: 



Probably nine-tenths of the forms of bacteria already described might as well 

 be forgotten or be 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 sufficiently described forms. 



The variations which occur and the very incomplete descriptions 

 which can be found make it impossible to identify many species even 

 to a more or less restricted group. For these reasons some of the 

 cultures are not identified or named, but letters are used for conven- 

 ience in this paper to represent the specific part. Migula's classifica- 

 tion has been used. 



The Cultures Which, are Described. 



Plate cultures were observed for some weeks, the different kinds of 

 colonies which appeared being especially noted. Subcultures were 

 then made in bouillon, and after 24 hours the subculture was re- 

 plated. Subculturing and replating were then repeated. From this 

 last plate the pure culture was made on agar for study. These were 

 not studied culturally, as a rule, for some weeks, thus allowing time 

 for the organism to eliminate any character due to recent environ- 

 mental conditions (1)." 



Morphology, Staining Properties, and Oxygen Requirements, with Sug- 

 gestions on Variations. 



(a) Size. — The length and thickness of a micro-organism often 

 varies so much with its environmental conditions that certain re- 



« Numbers in parentheses refer to papers in the bibliography at the end of 

 Part I or that at the end of Part II. 



