FORMS OF BACTERIA 



IY. Spirochaete. Spiral organisms which move by undulations of 

 their body and not by means of cilia (Fig. 13). Each Spirochaete 

 organism consists usually of a large number of twists. 1 



FIG. 10. Spirosoma. 



FIG. 11. Microspira. 



FIG. 12. Spirillum, showing cilia. 



This concludes the list of what may be designated as Bacteria in 

 the narrower sense of the term. There are, however, a number of 

 other organisms which are placed among 

 the bacteria, These represent a higher 

 form of development, because they show 

 a more complex type of structure and in 

 many cases a banding together of indi- 

 viduals to form a community. These 

 organisms are usually regarded as form- 

 ing the group Chlamydobaeteriaceae. 

 We shall mention here a few of the 

 more common types in order to show 

 the variety of forms which they can 

 assume, leaving to later sections a fuller 

 description of their life-histories and physiological characteristics. 



FIG. 13. Spirochaete. 



l lt is extremely doubtful whether the members of the genus Bacterium are 

 always motionless. In all the forms examined by the author it has been found 

 possible to induce motility by cultivating them under conditions in which they 

 were in contact with their own excretion-products as little as possible. If such 

 be the case, the distinction between Bacterium and Bacillus is done away with 

 (Centralblatt fur Bakteriologie, Abth. ii., 1903). * 



