THE STORY OF THE BACTERIA. 



weaker neighbors as the food grows scanty in 

 their microscopic seas, and the weaker goes to 

 the wall. 



Many forms possess the power of living and 

 multiplying in the manner described above so 

 long as the proper conditions prevail, but when 

 life, owing to some change in the environment 

 becomes no longer possible, the vital powers 

 collect themselves in a little shining mass in 

 one end of the bacterium, which surrounds 

 itself by a dense membrane, and in this form, 

 which is called a spore, the individual can sur- 

 vive adverse conditions which in the ordinary 

 form would have destroyed its life. Restore 

 it to the needed conditions and the spore 

 swells into a bacterium again, and the roots of 

 a new ancestral tree begin to sprout. 



These bacteria are really very simple forms 

 of cells, and like the cells which we have looked 

 at in the last chapter, their life expresses itself 

 in certain activities ; they move, they nourish 

 themselves and grow, they reproduce their 

 kind. They have the power in carrying on 

 the processes of their own nutrition, when 

 moisture and air are present, of tearing to 



