THE EARTHWORM IN SCIENTIFIC LITERATURE 53 



repetition. And, moreover, the entire mass of mould on every 

 field passes in the course of a few years through their alimentary 

 canals." 



In considering the significance of the above quotations and 

 comments, we will point out that in the example we have given 

 of the action of the earthworms in the Anglo-Egyptian Sudan, 

 the accession of ammonia to the topsoil would be an almost un- 

 believable amount. We can only surmise at this point that the 

 accession of other plant food elements to the topsoil is propor- 

 tional to the gain in nitrogen derived from ammonia. 



The constant translocation of the plant food minerals from 

 the subsoil to the surface zones, the thorough and ceaseless mix- 

 ing of these elements with the soil, making it a finely conditioned, 

 evenly balanced soil without the necessity for long weathering, 

 is just part of the important work oS worms. Without quoting 

 long references and details, let us summarize in part the v/ork 

 of earthworms in nature, with some related points, before pass- 

 ing on to the second part of the book, which deals with the con- 

 trolled activity of earthworms. 



SUMMARY 



Earthworms are found in nature, ranging from a sparse 

 population of a few thousand per acre to several millions per 

 acre in favorable environment. They are distributed prac- 

 tically all over the globe. 



While earthworms inhabit the surface layers of soil, de- 

 riving nutrition from the organic content of the soil, but swal- 

 lowing the soil with all that it contains, they commonly burrow 

 deep into the earth, riddling and honeycombing the earth to a 

 depth of several feet. They come to the top to deposit their 

 castings on top of the earth and in the loose surface layers, 

 bringing the subsoil to the top and mixing it with the surface 

 soil. In its passage through the worm, the mineral subsoil under- 

 goes chemical changes, making it immediately available for plant 



