GENESIS OF THE SOIL AND ITS POSSIBILITIES 183 

 carried by the water and assists in its solvent action. 



THE BOLE OF EARTH WORMS. 



" Of animal organisms those most active in the forma- 

 tion of soil are earth-worms. The work of earth-worms 

 in soil forming has been exhaustively studied by Dar- 

 win. The worms not only modify the soil by bringing 

 to the surface portions of the subsoil, but also influence 

 its physical state by making it more porous and pul- 

 verulent. According to Darwin, the intestinal content 

 of worms has an acid reaction, and this has an effect 

 on those portions of the soil passing through their ali- 

 mentary canal. The acids, which are formed in the 

 upper part of the digestive canal, are neutralized by 

 the carbonate of lime secreted by the calciferous glands 

 of the worms, thus neutralizing the free acid and chang- 

 ing the reaction to alkaline in the lower part of the 

 canal. 



" The worms further modify the composition of the 

 soil by drawing leaves and other organic matter into 

 their holes, and leaving therein a portion of such mat- 

 ter which is gradually converted into humus. Darwin 

 estimates that about eleven tons of organic matter per 

 acre are annually added to the soil in regions where 

 worms abound. A considerable portion of the am- 

 monia in the soil at any given time may also be due to 

 the action of worms, as much as 0.18 per cent, of this 

 substance having been found in their excrement. It is 

 probable that nearly the whole of the vegetable matter in 

 the soil passes sooner or later through the alimentary 

 canals of these ceaseless soil builders, and is converted 

 into the form of humus. Finally the bodies of the 

 worms serve to increase the quantity of the organic mat- 

 ter in the soil. 



