DISPOSAL OF SEWAGE 517 



608. Summary. The principal points to be remembered in 

 regard to the use of the septic tank are the following : 



1. The sewage must be disposed of while yet reasonably 

 fresh and inoffensive. 



2. To do so, it must be conveyed at once to the septic tank 

 where the solids in it are liquefied by anaerobic bacteria. It 

 must then be spread in a thin layer upon the surface of the soil, 

 or aUowed to pass into the upper layers of the soil, or into con- 

 tact beds, in such a manner that aerobic bacteria will quickly 

 act upon it, completely oxidizing and mineralizing it. 



3. The mechanical appliances used are simply such as will 

 most easily and certainly accomplish these results. 



