WATER SOLVENT ACTION OF WATER, ETC. 49 



warmth, moisture, decaying organic matter, cultivation, 

 aeration, and freezing as the most important ones. An 

 abundant supply of organic matter in a soil, its proper 

 cultivation to allow an abundant circulation of air, an 

 abundant supply of moisture, avoiding an excess, and 

 warm weather are the conditions best suited for nitrifi- 

 cation. The effects of frost and winds are mainly physical, 



Shallow 

 Dug Well 



Shallow 

 Bored Well 



Deep 

 Dug Well 



Deep 

 Bored Well 



Barren Stratum 



FIG. 14. Driven and dug wells showing the relative danger of drain- 

 age contamination. (Farmers' Bulletin 549, U. S. Dept. Agr.) 



and result in more finely divided soil particles, affording 

 more surface area for the activities of the natural solvents. 



43. Drinking Water. Impure water transmits many 

 diseases, among which may be mentioned typhoid fever, 

 dysentery, other diarrhoeal affections, cholera, cholera in- 

 fantum, animal parasitic diseases, enteric fever, tuber- 

 culosis, and scarlet fever. Typhoid fever may also be 

 spread by milk, raw fruit, shell fish, or flies. Scarlet fever 



