96 THE STORY OF GERM LIFE. 



become incorporated into the soil, the final result 

 being that the body of the plant or animal disap- 

 pears as such, and its substance is converted into 

 gaseous form, which is dissipated in the air or into 

 simple compounds which sink into the earth. 



This whole process of decay of organic life is 

 one in which bacteria play the most important 

 part. In the case of the 'decomposition of the 

 woody matter of the tree trunk, the process is be- 

 gun by the agency of moulds, for this group of 

 organisms alone appears to be capable of attack- 

 ing such hard woody structure. The later part 

 of the decay, however, is largely carried on by 

 bacterial life. In the decomposition of the ani- 

 mal tissues, bacteria alone are the agents. Thus 

 the process by which organic matter is dissipated 

 into the air or incorporated into the soil is one 

 which is primarily presided over by bacterial 

 life. 



Viewing this matter in a purely mechanical 

 light, the importance of bacteria in thus acting as 

 scavengers can hardly be overestimated. If we 

 think for a moment of the condition of the world 

 were there no such decomposing agents to rid the 

 earth's surface of the dead bodies of animals and 

 plants, we shall see that long since the earth 

 would have been uninhabitable. If the dead 

 bodies of plants and animals of past ages simply 

 accumulated on the surface of the ground with- 

 out any forces to reduce them into simple com- 

 pounds for dissipation, by their very bulk they 

 would have long since completely covered the 

 surface of the earth so as to afford no possible 

 room for further growth of plants and animals. 

 In a purely mechanical way, then, bacteria as de- 

 composition agents are necessary to keep the sur- 



