CHAPTER II 



CHARACTER OF BACTERIA 



BACTERIA are extremely minute living organisms. 

 Seen under a powerful microscope they appear as little 

 rods, spheres, or spirals. It is difficult for one unaccus- 

 tomed to the use of a microscope to conceive of the size 

 of these micro-organisms. They vary in size from 5^ 

 to ^ inch, so that a tiny drop of pus often con- 

 tains many thousand bacteria. Even a minute dust 

 mote floating in the air may carry them. Bacteria are 

 one-celled organisms, i. e., each cell is a complete in- 

 dividual. There is no head, no tail, and not even the 



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Fig. 1. Comparative size of human red blood-corpuscle, typhoid 

 bacillus, and influenza bacillus (Jordan). 



most powerful microscope reveals any special organs 

 within the cell. The mode of life of bacteria is the 

 simplest that can be conceived. Placed in suitable 

 surroundings, a bacterium after a time divides and 

 forms two bacteria. Each of these grows a little until 

 of the size of the parent, and then, in turn, it also divides, 

 forming two. And so the process goes on, each division 

 giving rise to two bacteria in the place of one. Under 

 proper conditions certain bacteria multiply very rapidly, 



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