CHAPTER IV. 

 CLASSIFICATION OF BACTERIA. 



THE difficulties inherent in the classification of bacteria are 

 numerous and, due to the small simple structure of the organism, 

 cannot be worked out on a purely morphological basis as is the 

 case with the higher plant. Moreover, physiological characteristics, 

 such as pigment production which at first sight may appear useful 

 are not constant. Even morphology of bacteria was not considered 

 constant until 1872 at which date Cohn established upon mor- 

 phological bases a classification which with minor changes has been 

 retained until the present. Bacteria play a part in many fields of 

 activity, and hence the criteria whereby they are recognized vary 

 greatly according to the art or science in which they are studied. 

 This has led to considerable confusion in classification and nomen- 

 clature as is so admirably pointed out by Jordan. 



"The present nomenclature of bacteriology may be criticized 

 on two grounds: first, as already pointed out, for the unwieldy 

 size that certain 'genera' have been allowed to assume; and second, 

 for the haphazard way in which trinomial and even quadrinomial 

 names have been bestowed. Such names can be properly employed 

 only with reference to subspecies or varieties; and designations, like 

 B. coli communis, Granulobacillus saccharobujxyicus mobilis non- 

 liquefaciens and Micrococcus acidi paralactici liquefaciens Halensi, 

 are both cumbersome and unscientific. The use of a single genus 

 name for a multitude of organisms is in fact responsible for the 

 tendency toward trinomial nomenclature, and the remedy for both 

 conditions would seem to lie in the abandonment of such a term as 

 Bacillus for the name of a genus and the frank establishment of 

 new genera on the basis of physiological characters, such, for example 

 as distinguish the colon-typhoid group or the diphtheria group of 

 bacilli. Until some such reform in -nomenclature is brought about 

 the names used to designate different kinds of bacteria will fail to 

 make clear the group relationships which undoubtedly exist, and 

 will continue to be a stumbling block to all students of the subject." 



The classification most commonly accepted at the present day 

 is that formulated by Migula. This, with certain modifications, is 

 given below. 



Bacteria, Schizomycetes, fission fungi (chlorophyll-free), cell divi- 

 sion in one, two or three planes; many varieties possess the power 

 of forming endospores. Whenever motility is present, it is due to 

 flagella, or more rarely to undulating membranes. 



