4IO SWINE IN AMERICA 



they pass further down they are restrained only by the 

 mechanical action of the earth. If, however, a soil be- 

 comes saturated with germs, as for example in a barn- 

 3'ard, or if the pollution is delivered below the surface, 

 as in a cess-vault, little purification will take place and 

 the germs may find their way into nearby wells. In 

 order to be certain of the water supply, wells should 

 penetrate an impermeable layer of earth, and the sides 

 be perfectly sealed, as with the iron tubular forms, so 

 that no water can gain entrance except from below. 

 A tubular well 20 feet deep is a much deeper well, from 

 a sanitary standpoint, than a dug well of the same depth. 

 It is also true that a shallow well may produce pure 

 water at one time and afterwards become contaminated 

 because of the saturation of the soil with germs, either 

 by the barnyard or vault.'' 



The Indiana station has made tests to obtain an idea 

 of the number of germs which may be found in water, 

 and the following table (Bulletin No. 70) shows the 

 range in number of germs found in a cubic centimeter, 

 v/hich is about one-half thimbleful: 



NUMBER OF 

 SOURCE. r.ERMS PER CU. CSI. 



Very filthy hog wallow 2,680.000 



Ordinary hog wallow 730.000 to 1,420.000 



Wabash river about LaFayette 12,000 to 32.000 



^\"abash river below LaFayette 112.000 to 390,000 



Clean looking pond 290,000 



Filthy watering trough 248,000 



Stock troughs 5,000 to 21,000 



