26 SPECIAL CHARACTERS 



The new forms may leave each other. or may adhere in 

 more or less characteristic groupings, which are taken advan- 

 tage of in their study and identification. Thus cocci may 

 form pairs or chains, and are known as diplo- or streptococci. 

 Again, the spheres may produce irregular grape-like bunches 

 or staphylococci. These develop in only two planes. Division 

 may occur in the third plane so that packets or cubes of 

 cells result, called sarcince. Among the rod-shaped bacilli 

 long chains may be formed by a continuous development in 

 the same plane. 



A single bacterial cell will divide about every twenty 

 minutes, and Fischer says that from one organism 16,000,- 

 000,000 may develop in a single day on suitable medium. 

 Fortunately, however, foodstuff is used up in the course of 

 multiplication and the waste products of nutritional activity 

 accumulate so that the enormous growth of bacteria is 

 limited. Bacteria can no better live in the presence of their 

 excretions than can animals. 



SPECIAL CHARACTERS. 



The cell sometimes surrounds itself by an envelope or 

 capsule outside its natural wall, and this is taken advantage 

 of in identification. It is particularly well developed on 

 bacteria when in or lately removed from animal tissues upon 

 which they have been growing. The exact function or 

 importance of these capsules is not known. 



Some bacteria are able to move from place to place in a 

 fluid medium, and are called, therefore, motile. This is due 

 to the presence of extremely fine filamentous extensions 

 from the cell wall, which upon microscopic examination 

 look like wavy hairs. These are called flagella (sing., flagel- 

 lum). They are arranged either at one end, both ends, or 

 around the whole surface of the cell. They propel the 

 bacterium by a quick waving or lashing motion. 



When bacteria are subjected to conditions unfavorable 



