REPRODUCTION 27 



in three planes. In size microorganisms vary consider- 

 ably. Perhaps a proper conception of some organisms 

 can be obtained when one considers that to cover one 

 square inch in single layer it would require 6,250,000,000 

 influenza bacilli, a very small organism, or 45,000,000 

 anthrax bacilli, a bacterium of moderate size. Bacteria 

 are measured in terms of microns. The metric unit, 

 a micron, equals about 2Tlro ^ of an inch. 



REPRODUCTION. 



Bacteria. Bacteria multiply by a simple dividing 

 of their protoplasm. The spherical organisms divide 

 much as one cuts an apple through the poles, the 

 divided halves rapidly assuming the shape of the 

 mother cell. The rods and spirals divide by simple 

 transverse pinching in at about the middle of their 

 long axis. 



The new forms may leave each other or may adhere 

 in more or less characteristic groupings, which are 

 taken advantage of in their study and identification. 

 Thus cocci may form pairs or chains, and are known 

 as diplo- or streptococci. Again, the spheres may pro- 

 duce 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 sarcincB. 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 



