FORM AND STRUCTURE OF BACTERIA 15 



the various species of bacteria be grown on standard media. 

 The variation in form and structure is often slight with some 

 species and pronounced in others. Bacteria are conveniently 

 divided into two orders, the Eubacteria (Migula), or true 

 bacteria, and the Thiobacteria, or sulphur bacteria. The 

 true bacteria, with which we are chiefly concerned, may be con- 

 veniently divided into two suborders, a lower and simpler 

 form known as the Haplobacteria (Fischer), and a higher 

 and more complex form called the Trichobacteria (Fischer). 

 Bacteria vary greatly in shape according to the genera and 

 species. 



Haplobacteria or Lower Bacteria 



The different form types of the haplobacteria are shown 

 in Fig. 4. 



Cocci. In the active or vegetative stage all the lower bac- 

 teria are composed of single cells of minute size. The simplest 

 of these is a round ball-like or globular form in which all the 

 diameters are equal. To this form type the term " coccus" has 

 been given. The group is subdivided according to the char- 

 acteristic method in which the cocci reproduce in different 

 planes (Chap. VI). If a coccus divides so that its successive 

 division walls are parallel, the result is a chain of cocci. Cocci 

 which reproduce in this manner are called streptococci (Ex. 

 Strep, pyogenes) (Fig. 5). The individual cocci in the genSr 

 streptococcus remain connected or glued together in a chain 

 by a gelatinous secretion. If a coccus divides in two direc- 



