FOODS 33 



water is decaying matter. Decaying slops from the house 

 or barnyard are very poisonous. They sometimes soak 

 into the well and poison the family. Disease germs can- 

 not grow in pure water, but they easily grow in water 

 containing decayed substances. Sometimes the germs of 

 typhoid fever get into the water of a well and grow, pro- 

 ducing the disease in those who drink the water. Water 

 may be impure even if it tastes good and looks clear and 

 sparkling. The surest way to keep the water pure is to 

 locate the well so that no slops or barnyard drainage can 

 reach it. 



59. How to purify water. If impure water must be 

 used, the disease germs may be destroyed by boiling it for 

 ten minutes. This also drives out the air and makes the 

 water taste flat, but if it stands a few hours, it takes up 

 air and becomes fit for use. Water can be somewhat 

 purified by passing it through sand or powdered charcoal 

 or some other powdered substance. An arrangement for 

 this purpose is a filter. A filter removes mud and coarse 

 particles, but it does not take out all the disease germs. 



60. Amount of water needed. A grown person needs 

 about three quarts of water daily. He will take half of 

 this with his solid food, leaving about a quart and a half 

 to be drunk extra. We should drink about this amount of 

 water daily. The time of drinking is not of great impor- 

 tance. Some should be taken at meal times, and, if the 

 meal is eaten slowly, it can do no harm. All drinks, of 

 course, contain water which should be counted as so much 

 ordinary water. 



61. Tea and coffee. Tea and coffee are not food, but 

 they act upon the mind so that the body does not feel tired 

 when hard work is done. By using a large amount of tea 

 and coffee it would seem that more work can be done, yet 



ov. PHYSIOL. (INTER.) 3 



