1 66 AGRICULTURAL BACTERIOLOGY. 



number of diseases actually distributed by water is very 

 small. Only two of our common diseases are known to 

 be frequently distributed by water. The most important of 

 these is typhoid fever, in regard to which the evidence is 

 abundant and most conclusive. This evidence need not be 

 given here, but it is sufficient to demonstrate that typhoid 

 fever is very commonly acquired by drinking water, that the 

 danger comes wholly from water which has in some way be- 

 come contaminated with human excrement, usually through 

 sewage, and that the drinking of sewage-contaminated water is 

 probably the most prolific source of this dreaded and serious 

 disease. 



The second water-borne disease is rarely of much signifi- 

 cance in agricultural communities. It has been abundantly 

 proved, in recent years, that Asiatic cholera is often distributed 

 by means of drinking water which has become contaminated 

 with the cholera germ. 



Besides these there are one or two other obscure diseases 

 of the alimentary canal, usually characterized by diarrhceal 

 symptoms, believed to be water-borne. 



The ordinary bacteria in water are of no significance what- 

 ever, either in their relation to health or to agricultural 

 processes. But from what has been said it is evidently a 

 matter of the greatest importance that drinking water should 

 be kept free from sewage contamination. While any kind of 

 pollution of drinking water is, of course, unfortunate, sewage 

 contamination is almost certain to be fatal to some of the 

 many persons using such water for drinking purposes. The 

 inhabitant of the city has no means of guarding against such 

 contamination. He can simply put the matter into the hands 

 of officials and must trust to their wisdom in securing a 

 proper supply. But the agriculturist commonly controls his 

 own water supply, and he must depend upon himself to keep 

 it properly guarded. If his supply is in the form of a spring, 



