142 GENERAL BIOLOGY OF MICRO-ORGANISMS 



mine their relationships. A few of them are important patho- 

 genic agents. 



The Lower Bacteria. The lower bacteria, or true bacteria, 

 are always simple in form, the transverse division producing 

 cells, relatively short, and of nearly equal length. Long filaments 

 are produced only by the attachment of many individual cells 

 together, end to end. There are no special fruit organs. The 

 special resistant form, or spore, which occurs in some forms is 

 produced only inside of the vegetative cell, one cell producing 

 one spore. There are three general forms of bacteria, the sphere 

 (coccus, plural cocci), the cylinder (bacillus, plural bacilli), and 

 the spiral or segment of a spiral (spirillum, plural spirilla). In- 

 termediate forms occur, so that there is not a sharp line between 

 the groups. These three forms are generally accepted as a basis 

 for division of the lower bacteria into three families, the coccaceae, 

 bacteriaceae and the spirillaceae. 



Spherical Bacteria. The Coccacea or cocci are spherical 

 bacteria. They vary in size from about 0.3^ to 3^ in diameter. 



Staphylococci. Streptococci. Diplococci. Tetrads. Sarcinae. 



FIG. 62. 



During the process of cell division, a coccus may become elongated 

 somewhat, and after division, the daughter cells may be shortened 

 so that they appear as if compressed against each other. Slightly 

 elongated forms are included among the cocci in certain instances, 

 and especially the lancet-shaped bacteria such as the germ of 

 lobar pneumonia. The recognition of genera within the family 

 is still unsettled. Morphologically five genera have been dis- 

 tinguished by Migula: Streptococcus, Micrococcus, Sarcina, Piano- 

 coccus and Planosarcina. The first three do not possess flagella 

 and are non-motile. Streptococcus includes those forms which 

 divide only in one plane so that a thread or chain is produced. 

 Micrococcus includes the cocci which divide in two planes at 



