QUALITIES AND KINDS OF WATER. 175 



It is not known that water is decomposed in the animal system. 

 Liebig says the tissues of vegetables are derived from water, thus 

 exerting a vital influence throughout the vegetable kingdom. The 

 tissues of the body are also modified and rendered flexible by it. It 

 aids digestion by acting as a solvent, and is instrumental in convert- 

 ing acids into urea in most animals, birds and reptiles excepted. It 

 combines chemically in converting the sugur of cane or starch into 

 the sugar of milk, and in other combinations in the animal economy. 

 It is used in many diseases as a dietetical remedy, and in numerous 

 ways holding in solution nutritive food. But its use is restricted in 

 what is called a dry diet, to limit the fluidity of the blood and retrench 

 circulation in valvular diseases of the heart, by affecting the coagula- 

 tion and deposition of fibrine. 



The quality of water is of the greatest importance to the health of 

 plants and animals. It is divided into common water, as used in or- 

 dinary drinks, and for domestic purposes, sea water and mineral water. 

 Distilled water may be obtained from any one of these. Common wa- 

 ter is known as well or pump, river, spring, lake and marsh waters. 

 Rain water is the purest of these waters ; it is, however, much less 

 pure at the beginning of a shower than after raining a few hours, as 

 it at first brings down the impurities suspended in the atmosphere. It 

 contains at all times a portion of air, and generally a portion of car- 

 bonate of ammonia, yielded to the air by decomposing organic substan- 

 ces, as we have mentioned in the last chapter. It is this ammonia 

 which affords nitrogen to plants, renders water soft, &c. Other sub- 

 stances, such as metalic and earthy salts, are also found in rain water, 

 especially when it first falls. 



Rain water in cities, if collected from the roofs of houses, has im- 

 purities, and should be boiled and strained before use. Snow water is 

 devoid of air and other gaseous principles, and hence fishes will not 

 live in it. When in the state of snow it does not quench thirst, bat 

 increases it, hence the people of northern regions suffer extreme thirst 

 rather than eat it; but when melted it allays thirst like other waters. 

 Spring water is rain water which has passed through the earth and 

 appeared again at its level on the side of a hill or mountain. It usually 

 takes up in its passase earthy salts and such other soluble matter as 

 the soil contains. River water is both rain and spring water, com- 

 monly holding in suspension several impurities, especially decomposing 

 vegetable substances, oftentimes in sufficient quantities to have dele- 

 terious effects, as commonly recognized in producing a relaxation of 

 the bowels, dysentary, &c. 



" An analysis of the Croton water of New York gives in 1 gallon, 

 carbonate of lime 1.52 grs., sulphate of lime .44, chloride of calcium 

 and of magnesium .90, carbonate of magnesia .84, with traces of 

 vegetable matter and iron total of solid matter 4.16 grs. in the gall. 



