18 A MANUAL OF BACTERIOLOGY 



is now but little used in this sense, and any straight rod 

 is termed a bacillus. The term " staphylococcus " 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 simple 

 curved rod is now known as a vibrio, a definitely cork- 

 screw form of three or a few turns is a spirillum, a long and 

 flexible twisted filament is a spirochaeta. The systematic 

 position of the Spirochaetse has given rise to controversy. 

 The parasitic ones (e.g. that of relapsing fever) are com- 

 monly 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 : 



r Trichobacteria ( occ id * a 



{itaL^saa: 



v SPIRO CHAETOIDEA 



\Cristispira 

 Saprospira 



Another classification is that proposed by Migula. 2 

 The Bacteria are divided into two orders : the Eubacteria 

 bacteria proper the cells of which contain neither 

 sulphur granules nor a colouring matter, bacterio-purpurin ; 

 and the Thiobacteria, the cells of which contain sulphur 

 granules and may be coloured with bacterio-purpurin. 

 The Eubacteria are divided into five families : (1) Coccacese, 

 (2) Bacteriaceae, (3) Spirillacea3, (4) Chlamydo-bacteriaceae, 

 and (5) Beggiatoacea3. These, again, are subdivided into 

 many genera, based partly on the mode of division and 

 partly on the number and on the arrangement of the 

 flagella upon the organisms. The Coccacese globular cells 

 contain the genera Streptococcus, Micrococcus, Sarcina 

 (non-motile), and Planococcus and Planosarcina (motile) ; 

 the Bacteriaceae are defined as long or short cylindrical 



1 Proc. Roy. Soc. Lond., B, vol. 85, 1912, p. 186. 



2 System der Bakterien, 1897. 



