THE BIOLOGICAL UNIT 47 



ments, so that It is evident that all living organisms 

 must draw their supplies from the same source. 

 When these chemical bodies have once become a 

 part of the body of a plant or animal, they are un- 

 available for any other plant or animal until re- 

 leased. The living organisms thus lock up in their 

 bodies a vast amount of material which is valuable 

 to other forms of life. As long as the organism 

 is alive, it is necessary that this material remain 

 in it, as it constitutes the material substance of its 

 body. But when death ensues, it can play no 

 further part in the life of the organism. This 

 material substance, however, would forever re- 

 main inaccessible were it not for the work of these 

 microscopic bacteria. The sparrow or the tree 

 that falls to the ground is immediately preyed 

 upon by numerous animals and plants until a shape- 

 less mass has taken the place of each. In this 

 transition many changes have occurred, the most 

 important of which bacteria and other fungi pro- 

 duce. Their work results in a simplification of 

 the complex bodies which the sparrow and the tree 

 had so carefully and elaborately built up. The 

 simplification continues until the body of each re- 

 turns to the air and soil from whence It originally 

 came. The body of man forms no exception to 

 this process. "Dust thou art and to dust re- 

 turnest," while not spoken of the soul Is most de- 

 cidedly the fate of the body. That the dead body 



