58 DAEWINISM AND HUMAN LIFE 



We follow the work further and it becomes 

 evident that the constant exposure of the soil 

 bacteria on the surface is bound to be important, 

 on the one hand, in allowing them to be scattered 

 by wind and rain, on the other in exposing 

 them to the beneficent action of the sunlight — 

 which is the most universal, effective, and eco- 

 nomical of aU germicides. 



In Yorubaland, on the West Coast of Africa, 

 Mr. Alvan Millson calculated that about 62,233 

 tons of subsoil are brought every year to the sur- 

 face of each square mile, and that every particle 

 of earth, to the depth of two feet, is brought to 

 the surface once in twenty-seven years. It need 

 hardly be added that the district is fertile and 

 healthy. 



Earthworms play their part in the disintegration 

 of rocks, letting the solvent humus-acids of the 

 soil down to the buried surface. Their castings 

 on the hiU-slopes are carried down by wind and 

 rain and go to swell the alluvium of the distant 

 vaUeys or the wasted treasures of the sea. The 

 well-known parallel ledges along the slopes of 

 grass-clad hills are partly due to earthworm 

 castings caught on sheep-tracks, and thus we 

 begin to connect the earthworms not only with 

 our wheat-supply but with our scenery. Well 

 may we say, with Darwin : " It may be doubted 

 whether there are many other animals which have 

 played so important a part in the history of the 

 world as have these lowly organised creatures." 

 Those who wish to understand Darwinism should 

 always begin with Darwin's last book — " The 

 Formation of Vegetable Mould through the Action 

 of Worms " (1881). It illustrates the web of hfe. 



