CLASSIFICATION OF BACTERIA. 9 



not interchangeable; so it is not possible for a coccus 

 to become a bacillus or a bacillus a spirillum. 



In order to see them it is necessary to use a 

 microscope of high magnifying power; indeed, it is 

 highly probable that some forms of bacteria are so 

 small that they cannot be seen with any of the micro- 

 scopes that we have. 



Bacteria reproduce by what is known as binary |^ e c p t 

 fission; that means a pinching off or splitting in the 

 middle, each part developing into another organism. 

 Reproduction occurs only under conditions favorable 

 for bacterial growth. The rate of division or multi- 

 plication is very fast, sometimes every fifteen minutes. 

 Starting with one organism one can imagine what an 

 enormous number may develop in twenty-four hours 

 at this rate. 



Under conditions unfavorable to the life and 

 growth some kinds of bacteria may assume another 

 form to avoid extermination. This is called spore 

 formation. These spores are round or oval bodies, 

 much smaller than the organism from which they 

 originate, and differ from them in having a thick 

 protective capsule that enables them to withstand 

 heat, sunlight and, in fact, any harmful influence. 

 The spores may be formed inside the body of the f o{?fa 

 organism and extruded from it, or the whole organ- 

 ism may be changed into a spore. As a rule, one 

 spore forms in each organism, but in some kinds of 

 bacteria several may be formed. When conditions 

 again become favorable for growth the spore may 



