CHAPTER IV 

 BACTERIA* 



The bacteria naturally fall into quite distinct groups or orders — 

 the true bacteria and the sulphur bacteria. 



A portion of the true or Eubacteria together with the sulphur form, 

 are designated as the higher bacteria. The forms usually spoken of 

 as bacteria belong to the group of lower bacteria, and when the 

 word "bacteria" alone is used reference is usually made to the lower 

 bacteria. These constitute a group of microorganisms quite distinct 

 and characteristic, while the higher bacteria form links, as it were, 

 between the lower bacteria and other closely related microorganisms. 

 The morphology of the two groups will need to be discussed 

 separately.* ' 



Forms or Lower Bacteria* 



Fundamental Form Types. — The forms of bacteria are exceed- 

 ingly simple. They are either spheres, straight rods, or bent rods 

 (spiral). In the spherical form they are known as cocci, or micrococci 

 (sing, coccus or micrococcus). The straight rods are bacilli (sing. 

 bacUlus) and the bent rods are spirilla (sing, spirillum). 



a; >•*' ^'s:: ffi 



Fig. 56. — Types of micrococci. {After Williams^ 



■9 





ji'jg_ j7._Xypes of bacilli. (After Williams.) 



•Preoared by W. D. Frost, with cytology by A. Guilliermond. 



77 



