16 Ilanual of Veterinary Microbiology. 



reason wells should not be built in proximity to cis- 

 terns, cess-pools or dung-hills. 



The deep waters best protected against infection 

 are those of artesian wells. 



Surface waters are always very rich in germs, the 

 nature of which is extremely variable ; the majority 

 are ubiquitous germs, pathogenic being much less fre- 

 quent. Stagnant waters especially favor the multipli- 

 cation of germs. 



Soil. — Whilst the rocks and the virgin soil from the 

 depths are free from all germs, these occur in large 

 numbers in the superficial layers. Their number and 

 nature vary infinitely according to location, season, 

 winds, the physical constitution and chemical com- 

 position of the soils, etc. Their multiplication grad- 

 ually decreases as the depth increases. Water, in 

 filtering through the ground, yields up the germs 

 which it contains as well as the soluble matters which 

 serve for their nutrition. 



It may be said, in truth, that germs in way of pul- 

 lulation, through their power of penetrating the cap- 

 illary spaces, should of themselves sink below the 

 layer of soil in which the waters deposit them. This 

 vegetation, however, is itself impeded by unfavorable 

 conditions of temperature and nutrition, the absence 

 of oxygen, etc. Hence in good filtering soil germs 

 are no longer found at a depth of three meters. 



Foods. — Vegetable foods (fodders, oats, etc.) are al- 

 ways contaminated with germs derived from the air, 

 the soil, or waters. Animal foods are generally con- 

 taminated by contact with the air. Foods, whether 

 of vegetable or animal origin, are especially favorable 

 to the multiplication of microbes. The various means 



