What Bacteria Do 21 



their bodies for only a comparatively short 

 time, the supply would run short and new 

 beings 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 known as putrefaction or decay 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, using a little of them 

 as may suit their own needs, and turning 

 over the rest to their earth neighbors, who 

 have got higher up the scale of being, but 

 not yet so far as not to need absolutely and 

 hourly oxygen, hydrogen, nitrogen, and carbon, 

 to keep their life's furnaces a-going. 



It is a very motley group of chemical 

 substances which these bacteria set free in 

 feeding themselves on nature's waste organic 

 materials. Sometimes these are very bad- 

 smelling gases, sometimes aromatic substances, 

 sometimes they are sweet, sometimes they are 



