CLASSIFICATION OF THE BACTKRIA 35 



somewhat elliptical. If the cells remain in contact after 

 division they are frequently flattened at the surface of 

 contact. They may form chains, packets or irregular 

 masses. Very few cocci are motile; none of the motile 

 species are of economic importance. Spores are not pro- 

 duced. Most of the genera of this family are parasitic, 

 many species are disease-producing. A few are of im- 

 portance because of the fermentative changes which they 

 bring about. The most important genera are Neisseria, 

 Streptococcus, Diplococcus, Staphylococcus, Micrococcus, 

 Sarcina} 



Neisseria. — The organisms of the genus are strict para- 

 sites, usually growing rather poorly in artificial culture 

 media. The cells usually occur in pairs, flattened at the 

 proximal sides, usually coffee-bean-shaped, and Gram-neg- 

 ative. Two of the diseases produced by organisms of this 



•*-» •* 



Fig. 14. — Neisseria. Fig. 15. — Streptococcus. 



group are of importance, namely, cerebrospinal meningitis, 

 and gonorrhea. 



Streptococcus. — This genus includes those spherical bac- 

 teria whose cells occur normally in chains. For the most 

 part the cells are Gram-positive. Certain of the species 

 are important in that they bring about lactic acid fermenta- 



1 Other genera are: Leuconostoc, forming large gelatinous masses 

 in sugar solutions; and Rhodococous, including the cocci which 

 produce a. red pigment. 



