220 Agricultural Bacteriology. 



house wastes. The cost of such a plant need not be more 

 than the city home must pay toward the construction of 

 the sewers of the city. 



The conditions that exist on the farms differ so greatly 

 that it is impossible to give a detailed description of a 

 disposal plant that will answer the needs of all farms. 

 In the following description, the essential conditions thai 

 must be established in order to have a successful plant 

 will be given. 



The house should be provided with a pressure tank, 

 either in the elevated form, or one in which the pressure 

 is maintained by compressed air, so that flushing arrange- 

 ments can be used in the water closets. 



Septic tanks. The sewage passes from the house 

 drain into a tank in which it is allowed to remain for sev- 

 eral days. The tank can best be made of concrete. It 

 should be placed beneath the ground so as to avoid freez- 

 ing. It should be large enough to hold the accumula- 

 tions of several days, since it is necessary that time be 

 given for the bacteria to decompose the solid matter. A 

 period of four days is sufficient, although a longer time 

 will have advantages. The amount of household sewage 

 will not exceed a barrel per day per person on the aver- 

 age farm. Thus a tank holding thirty to forty barrels 

 will suffice for a family of six persons. 



The sewage as it passes into the septic tank contains 

 much organic matter in solution and is in condition to 

 serve as bacterial food. The solid matter of the sewage 

 sinks to the bottom of the tank and is rendered soluble 

 by the continued bacterial action. On the surface of the 

 sewage a scum collects which shuts out all air and gives 

 favorable conditions for the growth of anaerobic bacteria. 

 The sewage as it flows from the tank after four or five 



