CLASSIFICATION OF BACTERIA 17 



considered by Lohnis and by Hort to be developmental 

 forms (see p. 13). 



Bacterial organisms may usually be grouped under one 

 of five forms. The cell may be (1) spherical, coccus, 

 (2) elongated and straight, bacillus, (3) elongated and 

 curved, vibrio, (4) elongated and twisted, spirillum, and 

 (5) long and filamentous, streptothrix : the last-named is 

 now frequently regarded as belonging to the Fungi and 

 not to the Bacteria. A streptothrix must be distinguished 

 from a chain of attached bacilli. 



Formerly a short rod was termed a bacterium, and a 

 long rod a bacillus, but such a division is an arbitrary one, 

 and at one stage of its life-history an organism might be 

 a bacterium and at another a bacillus. The term " bac- 

 terium " is now but little used in this sense, and any 

 straight rod is termed a bacillus. The term " staphylo- 

 coccus " is one frequently met with ; it is practically 

 synonymous with micrococcus, and refers to cocci which 

 are aggregated into groups or clusters. Of the twisted 

 rods, a definitely rigid spiral form of three or a few turns 

 is a spirillum, a flexuous twisted filament is a spirochaeta. 

 The systematic position of the Spirochaetae has given 

 rise to controversy. The parasitic ones (e.g. that of 

 relapsing fever) are commonly regarded as Protozoa, but 

 Dobell 1 dissents from this view and considers them all 

 to be much more closely allied to the Bacteria, which he 

 classifies as follows : 



SCHIZO- f Cyanophycese T . , , 



TiTT^rm A T TJ . ~, Tncho bacteria 



PHYTA 1 BACTERIA 



HAPLOBACTERIA { 



Coccoidea 

 Bacilloidea 



Spirilloidea / Spirochaeta 

 SPIRO 1 Treponema 



CHAETOIDEA 1 Cristispira 

 (Saprospira 



The following is an outline of Zopf's classification 

 (1885), the Bacteria being divided into four principal 



1 Proc. Roy. Soc. Lond., B ; vol. Ixxxv, 1912, p. 186. 



