CHAPTER XXXI 

 TECHNTCAL AND SANITARY PROBLEMS 



By GEORGE C. WHIPPLE 



Projessor of Sanitary Engineering, Harvard University 



There are several very practical problems of fresh-water biology 

 which deserve consideration, and which will be treated briefly in 

 this chapter. They relate chiefly to some of the smallest organisms 

 found in fresh water, — the bacteria and the plankton. There are 

 other problems, to be sure, which have to do with larger organisms, 

 but most of these have been referred to in the various chapters 

 which have gone before. 



First and foremost is the problem of disease transmission. Patho- 

 genic bacteria are not normally present in natural fresh waters, 

 but rivers and lakes in inhabited regions are subject to pollution 

 with the excrement of animals and human beings and such excre- 

 mentitious substances are liable to contain the germs of disease. 

 The adoption of the water carriage system of sewerage about the 

 middle of the nineteenth century greatly increased these chances 

 of fresh-water contamination. Water which contains excrementi- 

 tious matter or bacteria of fecal origin may be said to be con- 

 taminated; if bacteria are actually present the water is said to be 

 infected. The most noteworthy diseases which are water-borne 

 are typhoid fever, Asiatic cholera, and dysentery, but there are 

 other water-borne diseases, for contaminated water may contain the 

 spores of other bacteria, molds, and the ova of parasitic worms. 

 Fresh water also may serve as a medium within which mosquito 

 larvae grow and from which mosquitoes emerge. Special kinds of 

 mosquitoes play an important part in the transmission of yellow 

 fever and certain other diseases. Then there may be indirect as 

 well as direct relations between man and the microorganisms found 

 in water. 



Microscopic organisms form the basis of the food supply of 

 fishes and thus indirectly contribute to human sustenance. Oysters 



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