432 AGEICULTUEAL AND INDUSTEIAL BACTEKIOLOGY 



in man are typhoid fever, paratyphoid fever, Asiatic 

 cholera and dysentery (both amebic and bacillary). In 

 every case the organisms causing these diseases are forms 

 that multiply in the intestines of those who are infected and 

 can contaminate water only when the body excretions, that 

 is, the feces and urine of those harboring the organisms, 

 gain access. It is evident, therefore, that to a very great 

 extent these diseases are transmitted only by water which 

 contains excreta from those having the disease. 



Diseases of animals are not so frequently transmitted 

 through water. It is probable that occasionally animals, 

 drinking from brooks or streams which have, farther up in 

 their course, passed through farms where there are diseased 

 animals, may contract such diseases as hog cholera or an- 

 thrax. Certain diseases of the alimentary tract in some 

 respects closely resemble the paratyphoid fever of man and 

 may also be transmitted in the same fashion. 



The contamination of natural waters with considerable 

 quantities of putrescible material, particularly sewage, is 

 important also in other ways. The water of the streams 

 containing a large percentage of sewage of factory wastes 

 may become so polluted as to stop the development of the 

 normal water fauna. It has been recognized, for example, 

 that most of the so-called game fish will not live or develop 

 in water containing any considerable admixture of sewage. 

 Some fish can live in larger proportions, such as the carp. 

 The presence of sewage also prevents the growth of insects 

 and Crustacea which constitute the food for these fish. It 

 may also prevent the growth of the fresh water mussels or 

 clams so important as a source of supply of material for 

 manufacturing. 



Large quantities of sewage or other organic material, such 

 as factory wastes in the water of running streams, may also 

 create a nuisance as a result of putrefaction. The presence 

 of such organic matter in the water soon leads to the using 



