48 Manual of Veterinary Microbiology. 



The infection of subterranean waters by tbe soil is 

 subject to numerous influences dependent upon the 

 location and nature of the land. Changes of eleva- 

 tion of the surface waters also produce effects which 

 it is of importance to consider. It has been noticed 

 that large floods are often followed by typhoid epi- 

 demics, a circumstance which has been attributed to the 

 simultaneous rise in level of the waters of infiltration 

 generally, and especially adjoining large sheets of 

 surface water; this elevation of the subterranean wa- 

 ters brings them into contact with soils impregnated 

 with putrid matters in the neighborhood of cesspools, 

 trenches of liquid manure, sewers, etc., and when 

 these putrid matters contain the typhoid germ there 

 results a general pollution of springs and wells into 

 which these contaminated waters difiuse themselves. 



The pathogenic germs of the soil can retain their 

 vitality for a period more or less extended ; Grancher 

 has seen the typhoid bacillus retain its vitality in the 

 soil for five months. The charbon bacillus is also pre- 

 served in this medium, more especially, however, in 

 the form of spores. 



The destruction of these germs is dependent upon 

 the action of the oxygen and light ; as the conditions 

 of their puUulation are more delicate than those of 

 saprogenic microbes, the presence of the latter must 

 also be taken into consideration in so far as their ac- 

 tive proliferation more or less rapidly brings about an 

 insuflacient supply of nutrition for the pathogenic 

 species. 



Foods. — The vegetable foods may be contaminated 

 by pathogenic germs either by contact with the soil 

 while yet in growth (charbon, actiuomyces), or, after 



