204 BACTERIA IN AIR, SOIL, WATER, AND MILK 



in laboratory media, placing a part at ordinary tem- 

 perature and another at body temperature. By the 

 latter means the forms parasitic to animals are found. 

 Tetanus bacilli are, perhaps, the most wide-spread 

 of pathogenic bacteria in the soil. Their resistant 

 spores remain alive an unlimited time. Persons going 

 barefoot and subject to wounds or bruises may con- 

 tract the disease. Tubercle bacilli, in dead persons, 

 live only a few months, but when contained in sputum 

 spat upon the earth survive for a long period. 



BACTERIA IN WATER. 



In water there are many hundreds of species, but it 

 may be said in general that all the disease-producing 

 kinds are in water because discharges from human 

 disease have been put into it. Of course this may not 

 be direct, but through the agency of soil as mentioned 

 above. Some, bacteria may be carried into streams by 

 rain which brings down the dust, llain itself is free 

 of germs. Bacteria may be present in water up to the 

 billions without altering greatly its clearness or giving 

 it an odor, while, on the other hand, a cloudy water 

 does not necessarily indicate bacterial pollution, for 

 the turbidity may be due to harmless inorganic chemical 

 matter. Of the two water sources recognized by hygien- 

 ists, ground water (deep wells) and surface water 

 (ponds, lakes, and rivers), the second is by far the 

 more important and the more easily polluted. Large 

 bodies of water, either still or moving, tend to rid 

 themselves of bacteria. In still or slowly moving 

 bodies, such as reservoirs, germs settle with other 



