DISEASES OF CATTLE 47 



this process, and the liquid can then be discharged into an open 

 stream, with a great bulk of the running water, or into an irrigating 

 system. 



The process of decomposition in this septic tank is greatly aided 

 by using a great quantity of water. This is an advantage on dairy 

 farms, for water is used in abundance for washing utensils and 

 cleaning the cow barns. 



Plan of Disposing of Sewage After Liquefying. As stated 

 above, the sewage, after once being decomposed in a septic tank, 

 can be discharged into a running stream or river without emitting 

 offensive odors. This is the simplest way to dispose the sewage, but 

 there are many farms which are not located so as to allow the sew- 

 age to be discharged into such a stream. For such a farm, in fact 

 for every farm where it can be adopted, the disposal of sewage by 

 irrigation is by far the best method. There are two methods used 

 for irrigation: the surface method and the subsoil method. With 

 the surface method liquid sewage is drained through glazed tile to a 

 piece of ground set apart for this purpose. The ground is ridged 

 and the sewage is allowed to flow over the ground in shallow chan- 

 nels. The liquid slowly disappears by filtering through the soil. 

 Patches of ground that are wet must be carefully under-drained so 

 as to allow the surplus water to be drained from the surface. This 

 method of disposing sewage is objectionable from the standpoint 

 that the sewage flows on the surface and animals crossing such fields 

 may carry sewage on their feet, and if there are any disease germs 

 in the sewage it may be carried from one place to another. 



The safest method is sub-soil irrigation. This consists of a 

 system of underground porous tile, laid so as to allow the sewage to 

 seep through the tile. The tile are connected directly with a septic 

 tank and laid so as to leave approximately one-eighth of an inch be- 

 tween each tile in order to allow the sewage to seep through the tile 

 into the soil. The main line should consist of a five-inch tile, de- 

 pending somewhat upon the sewage. If a great amount of water is 

 used with sewage, four-inch tile may be used. The lateral drains 

 may be four-inch tile, or if the main drain is a four-inch tile the 

 laterals may be three inch. Nothing smaller than a three-inch tile 

 should be used for this purpose. 



For irrigation purposes tile should be laid from eight to sixteen 

 inches beneath the surface of the ground, with a gradual incline of 

 one or two inches for every one hundred feet. The depth to which 

 these tile should be laid depends on the nature of the soil. There 

 should be two systems for each septic tank. One of these systems 

 should be laid below the frost line for winter sewage disposal, while 

 the one laid shallow is used for summer disposal. By this method 

 the sewage which is so objectionable on the dairy farm or in the 

 creamery is removed and is used for irrigating and fertilizing pur- 

 poses. 



This surface method of sewage irrigation is particularly profit- 

 able for intensive farming and horticulture. The author knows of 

 a number of instances where in one year such a system has paid for 



