32 HUMAN PHYSIOLOGY CHAP. 



excellent precaution to take when there is reason to 

 suspect disease germs. How can it be purified ? There 

 is but one safe way to purify water containing disease 

 germs, and that is to boil it. If the temperature of 

 water is kept at the boiling point for about twenty min- 

 utes, all germs are destroyed, and when cooled it may 

 be safely taken into the stomach. The common water 

 filters are of value in removing the coarse substances, 

 and so making the water look clear and pure ; but they 

 cannot be relied upon to remove the germs that cause 

 disease unless they are properly cared for. 



In connection with bad water we must discuss ice. 

 Ice is just as impure as the water of which it was 

 formed, because freezing does not kill the disease 

 germs. Ice from lakes or rivers whose waters are 

 unfit for drinking purposes should not be put into 

 drinking water nor used in ice boxes in which foods are 

 kept. Serious diseases are often traced to the use of 

 impure ice. The excessive use of ice water is an 

 American habit that cannot be defended from the 

 standpoint of health. The temperature of substances 

 taken into the stomach should not be below 44 F. nor 

 above 131 F. 



35. Tea and Coffee. These are not foods, but have 

 become almost universal beverages with meals, in place 

 of water. Both contain substances that have a stimu- 

 lating effect upon the muscles and the nerves. Some 

 people use tea or coffee when very tired because 

 they make them feel better. This is because they re- 

 store muscular activity and stimulate the brain cells. 



