BACTERIA. 59 



thread, a full spiral of several turns is produced. Cell division takes place in only one 

 direction of space, and this is transverse to the long axis of the cell. 



Genus : Spirosoma MIGULA. 



The cells are rigid and bent in the form of spirals. The members of this genus are 

 as a general rule quite large. The cells may be free or united together into small 

 gelatinous masses. Some of the cells individually are surrounded by a gelatinous enve- 

 lopes, while others are free. 



Genus: Microspira SCHRO'TER. 



The cells are rigid, short, and bent similar to a comma. When the cells are united 

 together, S-shaped threads are formed. The cells are motile, possessing usually one 

 flagellum and rarely two or three flagella. These flagella are about the same length as 

 the cell. No endospores are formed. Some writers make no distinction between 

 Microspira and Spirillum. The name Vibrio has also been applied by some writers 

 to this genus. 



Genus : Spirillum EHRENBERG. 



The cells are rigid, usually long and forming long, screw-like threads, or, in some 

 cases, only portions of a spiral turn. Cells are motile and possess a tuft of flagella at 

 }he pole. The flagella may occur at both ends of the spiral, and they vary greatly 

 in number. Endospore formation has been observed in some species. 



Genus : Spirochaeta EHRENBERG. 



The cells are flexible spirals, very thin and long. No flagella are present. These 

 bacteria move by rotation similar to a screw, and also by lateral motion similar to 

 a snake. The locomotive organs, if present, are not known. No endospores are 

 produced. 



II. Suborder: Trichobacterinae (higher bacteria). 



Family : Chlamydobacteriaceae MIGULA. 



The cells are cylindrical, are united in threads, and surrounded by a sheath. 

 Reproduction takes place by means of motile and non-motile gonidia. These gonidia 

 arise directly from the vegetative cells and, without any resting stage, produce new 

 threads of cells, 



Genus : Chlamydothrix MIGULA. 



The cells are cylindrical, non-motile, and arranged in unbranched threads and 

 surrounded by a sheath of varying thickness in different species, being the same 

 diameter at apex and base (Fig. 39). Reproduction takes place by means of gonidia, 

 which are round and arise directly from the vegetative cell. This genus is called 

 Leptothrix by KUTZING and Streptohrix by COHN. 



Genus : Crenothrix COHN. 



The cells are united together into filaments which are unbranched. The filaments 

 gradually enlarge toward the free end, thus making a distinction between the apex and 

 base. The sheath which covers the filaments is thick and often becomes infiltrated 

 with the hydroxide of iron after being cast off in water in which there is a large amount 

 of iron. Reproduction takes place by the formation of round gonidia which are formed 

 in the beginning by division perpendicular to the long axis of the cell and later by divi- 

 sion in three directions of space. Only one or possibly two species can be placed in this 

 genus. 



