110 AGRICULTURAL BACTERIOLOGY 



through the sewers to the place of disposal. A considerable 

 amount of decomposition occurs in the sewers as the sewage 

 flows through them. The larger amount of decomposition 

 must, however, occur in the soil, in water-courses or in ar- 

 tificial disposal plants. In all, the same organisms function. 

 The sewage may be flooded over the land in a manner com- 

 parable to the application of water in irrigation. The 

 water leaches through the soil, leaving the organic matter 

 behind, there to be decomposed by the soil organisms. 

 Sandy land is desirable for the successful use of this 

 method of sewage disposal. From the open soil the water 

 passes quickly, while the air drawn into the pore spaces 

 facilitates the decomposition process. Within a short time 

 this change is effected. If a fresh application of sewage 

 is then made, the soluble products resulting from the first 

 will be removed, and another quantity of organic matter 

 will be left in the soil. 



The process can be continued indefinitely; for, owing to 

 the highly aerobic condition of the sand, decomposition is 

 complete. If an attempt is made to employ a close-grained 

 soil for such purposes, failure will result. The organic mat- 

 ter left by the percolating sewage will not be completely de- 

 composed, because of the small supply of oxygen, and the 

 residue will increase in amount. Soon the land will be- 

 come of no value for the disposal of sewage. The cities of 

 Berlin and Paris dispose of a portion of their sewage by 

 applying it to sandy land. The farm home can use this 

 same method with success if it is provided with a modern 

 water supply, so that water can be employed to carry the 

 sewage on to the land. 



In most cities the sewage is turned into a body of water, 

 and the decomposition processes occur in the liquid rather 

 than in the soil. If the body of water is large in proportion 

 to the volume of sewage, the decomposition will take place 



