20 THE STORY OF THE BACTERIA. 



pieces, in the chemical sense, dead organic 

 material, using up such parts of it as they need 

 for their own purposes, and setting free the 

 rest in such form as to be available for the use 

 of other living things. 



Everybody knows who thinks about it, that 

 the supply of such material as makes up the 

 bulk of the tissues of man, animals, and plants, 

 on this earth, is limited. So that if things were 

 not so arranged that living beings should have 

 the use of the material which goes to make up 

 their bodies for only a comparatively short 

 time, the supply would run short and new be- 

 ings could not continue to appear. 



When that mysterious group of activities 

 which we call life ceases to be manifested, in 

 animals and plants alike, if moisture and oxy- 

 gen and sufficient warmth are present, that 

 process which we know as putrefaction or de- 

 cay begins, by which the old combinations of 

 matter are broken up and the material set free 

 for the use of other beings. Now just here 

 enter the bacteria. It is they who tear these 

 old organic compounds asunder, use a little of 

 them as may suit their own needs, and turn 



