DIVISION II. 



MICROBIOLOGY OF WATER AND SEWAGE. 



CHAPTER I.* 

 MICROORGANISMS IN WATER.f 



Water is necessary in the life of man. Besides its use as a beverage, 

 for cooking, and all domestic purposes, it is largely used in many manu- 

 facturing industries; therefore, the study of its chemical and biological 

 content is one of the most important features of modern hygiene. All 

 natural waters contain microorganisms, which gain entrance 'from many 

 sources. 



Under the influence of the sun, sea water evaporates and forms a 

 water vapor, which we call clouds; and these, driven by the wind over the 

 land, are precipitated as rain and in the form of snow or hail. 



Most of this water collects from vast areas into brooks, streams, rivers, 

 lakes, or in subterranean streams, and finally reaches the sea whence it 

 came. 



The water vapor arising from the sea or land contains no organisms; 

 but as soon as the vapor is precipitated microorganisms find their way into 

 it. These come from the air and from the soil. Some of them find in 

 water sufficient nutriment for their life and growth; and, because of their 

 constant presence and evident ability to thrive in water, they are some- 

 times spoken of as belonging to the "water flora." Others, such as the soil 

 bacteria, are found only at certain seasons, as after rain or during flood- 



* Prepared by F. C. Harrison. 



f For specific details regarding methods of analysis and a fuller presentation of the subject, 

 readers may consult any of the following excellent books: 



1. Savage, W. G.: The Bacteriological Examination of Water Supplies, London, H. K 



Lewis, 1906. 



2. Horrocks, W H.: An Introduction to the Bacteriological Examination of Water, 



London, J. and H. Churchill, 1901. 



3. Prescott and Winslow: Elements of Water Bacteriology, and Ed. New York, Wiley 



& Sons, 1908. 



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