BACTERIA IN WATER 191 



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 widespread 

 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. Rain itself is nearly 

 free of germs. Bacteria may be present in water up 

 to the billions without altering greatly its clearness or 

 giving it an odor. Of the two water sources recognized 

 by hygienists, 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 

 organic and inorganic matters. For water-courses of 

 any character purification is aided by changes in 

 temperature during the day and night and the very 



