148 GENERAL BIOLOGY OE MKEO-ORGANISMS 



Many of them exhibit a differentiation of the' filament into base 

 and apex, some of them' branch in an irregular fashion, and in 

 some there is a suggestion of the formation of special fruit organs. 

 These higher bacteria require further study to determine their 

 relationships. A few of them are important pathogenic agents. 



The Lower Bacteria. — The lower bafcteria, 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 coccaces, 

 bacteriaceae and the spirillacese. 



Spherical Bacteria. — The Coccacea or cocci are spherical 

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



^ ^'P ^ 



Staphylococci. Streptococci. Diplococci. Tetrads. Sarcinae. 



Fig. 64. 



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, 



