GENERAL CHARACTERISTICS OF BACTERIA. 41 



a. Single coccus, grouped irregularly. 



b. Diplococcus, forming pairs. 



c. Streptococcus, forming chains, often showing 



paired cocci. 



d. Tetracoccus, forming fours by division through 



two planes of space. 



e. Sarcina, forming packets of eight members by 



division through three planes of space. 



2. Bacillus. Oblong or cylindrical forms, having 

 one dimension greater than any other, more or less 

 straight, and never forming spirals. 



a. Single bacillus. 



b. Diplobacillus and streptobacillus, forming twos 



or longer chains, the bacilli attached end to 

 end. 



c. Filaments, or thread-like growths, in which 



divisions into bacilli of the normal length 

 are not apparent, or occur irregularly and 

 transversely, to the long axis of the growth. 



3. Spirillum. Cylindrical and curved forms, con- 

 stituting complete spirals or portions of spirals. 



The determination of morphological characters for 

 the description of bacteria should always be made from 

 fully developed cultures; those which are too young 

 may present, as already noted, immature forms, due to 

 rapid multiplication, while in old cultures altered or 

 degenerated forms may be observed. 



When growth is obtained upon different media, varia- 

 tions, especially in size, may sometimes be observed. 

 These differences should always be described, together 

 with a note of the media upon which they were devel- 

 oped and a statement as to whether such variation is a 

 marked feature of the species under consideration. 



