Structure, Groivth and Distribution. 19 



tains larger numbers than country air. Wherever dried 

 fecal matter is present, as in barns, the air contains 

 many forms. 



Water generally contains enough organic matter in 

 solution, so that certain types of bacterial life find fav- 

 orable growth conditions. Water in contact with the 

 soil surface takes up many impurities, and is of neces- 

 sity rich in bacteria. As the rain water percolates into 

 the soil, it loses its germ content, so that the normal 

 ground water, like the deeper soil layers, contains prac- 

 tically no bacterial life. Springs, therefore, are rela- 

 tively deficient in germ life,' except as they become con- 

 taminated with soil organisms, as the water issues from 

 the ground. Wells vary in their germ content, depend- 

 ing upon manner of construction, ease of contamination 

 at surface, etc. Wells are too frequently insufficiently 

 protected from surface teachings, and consequently may 

 contain all kinds of organisms found in the surface soil. 

 Typhoid fever is very frequently disseminated in this 

 way, as is cholera and a number of animal maladies. 



While the inner tissues of healthy animals are free 

 from bacteria, the natural passages, as the respiratory 

 and digestive tracts, being in more direct contact, with 

 the exterior, become readily infected. This is partic- 

 ularly true with reference to the intestinal tract, and in 

 the undigested residue of the food, bacterial activity is 

 at a maximum. The result is that fecal matter of all 

 kinds contains enormous numbers of organisms so that 

 the pollution of any food medium, such as milk, with 

 such material is sure to introduce elements that seriously 

 affect its quality. 



