THE BACTERIA (SCHIZOMYCETES) 167 



use parts of them as food. The processes of securing this food 

 result in partial or complete breaking down of the food sub- 

 stance. This is known as decay. While a body is undergoing 

 decay, usually several kinds of bacteria and other organisms 

 live in turn upon it. In complete decay all of the nutrient 

 organism is used as food, passes into the air as gases, or is 

 dissolved in water and carried into the earth or into streams. 

 The materials that result from decay are not only directly the 

 remnants of the original plant or animal body, but may also 

 contain excretions from decay-producing organisms. Further- 

 more, many of these organisms of decay have themselves died 

 and decayed. 



Processes of decay are of great biological importance. It is 

 necessary to have the dead bodies and the waste products of 

 living bodies of plants and animals reduced to a form that 

 makes their removal possible. The materials that are broken 

 down are thus made usable for future growth of plants and 

 animals. Without decay, all usable food material would even- 

 tually be rendered unavailable for further growth of plants 

 and animals, so that life on the earth would cease. The earth's 

 supply of food materials would be locked up in organized plant 

 and animal bodies. 



155. Relation to agriculture and gardening. It has long been 

 known that the introduction of decayed and decaying organic 

 matter into soils enables them to sustain a more luxuriant 

 vegetation. Undecayed organic matter is not available for 

 those plants which we usually desire to grow. Such material 

 must await more complete disorganization before it can be 

 useful. It is desirable to regulate decay so that the largest 

 possible amount of its products may be retained in the soil. 

 This is one of the problems of scientific agriculture. For ex- 

 ample, if stable manure in large masses is allowed to " heat " 

 under the rapid destructive action of the bacteria and other 

 living things which flourish in it, much valuable ammonia is 

 given off into the atmosphere and lost. Slower decay, espe- 

 cially if underground, wastes but little ammonia. The bacteria 



