92 Bacteria in Relation to Country Life 



as the water-table. Wells are made by digging down 

 some feet into this saturated zone. 



It frequently happens that the cess-pool situated 

 at a distance of 25 feet or less from the well is made to 

 discharge its contents into the latter. The liquid from 

 the cess-pool, which is not as deep as the well, gradually 

 passes downward until the water-table is reached. 

 The air in the ground above the water-table offers 

 more or less resistance to the downward passage of the 

 sewage, and the latter will flow more readily towards 

 the points where the resistance is least'. The air in the 

 well, subject to expansion and contraction with changes 

 in temperature, causes the well to become the center of 

 least resistance, and encourages the inflow of water 

 from the surrounding soil. The removal of water from 

 the well also stimulates further additions from the 

 adjacent portions of the saturated zone. 



When cracks exist in the ground, the passage of 

 water into the well from the surrounding soil becomes 

 even more rapid, and, under such conditions, wells 

 have been known to become polluted from sources 

 several hundred feet distant. Should the cess-pool 

 receive additions of disease germs from the house, the 

 well-water nearby is then exposed to serious infection, — 

 the more so since, in sewage-polluted soil, the normal 

 soil bacteria are crowded back by the sewage bacteria, 

 and the disease germs may survive for a longer time 

 under such conditions. 



It is scarcely necessary to emphasize the evident 

 significance of these observations. They help us to vm- 

 derstand why it is so difficult to eradicate the disease, 



