CHAPTER XXVIII. 

 WATER BACTERIOLOGY. 



COMMON things are often little prized, and this is true of water. 

 Yet there is no other compound which plays so many and such 

 vital parts as does this substance. It composes two-thirds of the 

 body weight, entering into the make-up of every tissue. The 

 muscles which do our work contain 75 per cent, water; the liver 

 which acts as the body protector against poisons consists of 75 

 per cent.; the bones, which 4 possess a tensile strength of 25,000 

 pounds per square inch and are one and one-fourth times as strong 

 as cast-iron, consist of 40 per cent.; the brain, the most complicated 

 and wonderful organ of the body, consists of 85 to 90 per cent.; 

 the blood, that cosmopolitan fluid which visits every tissue of the 

 body bearing to it nutrients and from it waste products, contains 

 over 90 per cent, water. All the secretions of the digestive glands 

 consist mainly of water, and it is not there merely as a vehicle in 

 which are conveyed the active principles, for it enters into practi- 

 cally every chemical reaction through which carbohydrates, fats 

 and proteins pass in the process of digestion and metabolism. 

 It is the fluid in which are held the mineral nutrients which play 

 such a vital part in the life phenomena. Water gives to the tissues 

 their plumpness, carries off waste products, regulates the body 

 temperature and acts as a catalyzer in most reactions. Hence, a 

 substance which is of such vital importance and so often polluted 

 or infected must receive more than passing notice by the bacteri- 

 ologists. 



Classification of Waters. From a bacteriological viewpoint, 

 natural waters are best classified according to their relation to the 

 rich layers of bacterial growth upon the surface of the earth. There 

 are four distinct classes: (1) Atmospheric water, (2) surface waters, 

 (3) stored waters and (4) ground waters. 



1. Atmospheric water consists of rain and snow. It is really 

 water which has been vaporized and then condensed. It contains 

 none of the non-volatile substances and should, therefore, more 

 nearly approach pure water than any of the other natural sources. 

 But even this is far from pure, for as it falls through the atmosphere 

 it absorbs gases and collects large amounts of floating dirt. Every 

 one has observed how a shower will wash the air so that it becomes 

 beautifully clean and clear. The minute the water reaches the 



