CLASSIFICATION OF BACTERIA 33 



ing them according to their physiological and chemical activities. 

 Even this artificial procedure is unsatisfactory, for bacteriological 

 diagnosis is a subject which has developed under the stress of practical 

 needs, and as bacteria play a part in many fields of activity, it has 

 inevitably followed that the criteria whereby they are recognized 

 vary greatly according to the art or science in which they are contem- 

 plated. Even the same species may be identified by wholly different 

 characteristics. Notwithstanding the difficulties which surround the 

 grouping of bacteria, Migula 1 has worked out a system of classification 

 based upon purely morphological characteristics, which effects a 

 primary separation of bacteria into smaller subdivisions, which is 

 moderately satisfactory so far as it goes, and it is the one commonly 

 adopted. 

 With certain additions it is as follows: 



THE TRUE BACTERIA: EUBACTERIACE^E. 



1. Coccacece. Cells in the free state spherical. 



(a) Micrococcus. Cells spherical. No definite sequence of planes of septa- 



tion. 

 (6) Diplococcus. Organisms habitually occur in pairs. 



(c) Streptococcus. Plane of septation parallel. Form longer or shorter 



chains. 



(d) Tetracoccus. Planes of septation alternate, and at right angles in two 



plaices of space. Form groups of four or tetrads. 

 (e)' Sarcina. Planes of septation alternate, at right angles, in three planes 



of space. Form packets. 



(/) Planococcus. Motile cocci, provided with flagella. 

 (g) Planosarcina. Motile sarcina, provided with flagella. 



2. Bacillacece. Cells elongated and cylindrical; straight. 



(a) Bacterium. Non-motile. No flagella. 

 (6) Bacillus. Cells motile. Peritrichic flagellation. 



(c) Pseudomonas. Cells motile. Polar flagellation. Single flagellum or 

 tufts of flagella at one or both poles of the organism. 



3. Spirillacece. Cells elongated and cylindrical; spirally twisted about the long 



axis. 



(a) Spirasoma. Cells rigid and slightly curved; without flagella. 

 (6) Microspira. Cells rigid and slightly curved; with one, rarely several, 



polar flagella. 



(c) Spirillum. Cells rigid, loosely coiled; with tuft of polar flagella. 

 (d} Spirocheta. Qells flexuous, closely coiled; flagellation unknown. 



THE HIGHER BACTERIA. 



4. Chlamydobacteriacece. Cells enclosed in a sheath. 



(a) Streptothrix. Cell division always in one plane. 



(b) Phragmidothrix. Cell division in three planes of space; very delicate 



sheath. 



(c) Crenothrix. Cell division in three planes of space ; sheath well developed . 



(d) Cladothrix. Cells more or less branched. 



5. Beggiatoacece (Thiothrix). Cells contain sulphur granules. 



1 System d. Bakterien, Jena, 1907. 



