56 THE HUMAN BODY. 



17. Bad air is air that has lost its oxygen by being 

 breathed, or that has gases in it that do not belong to 

 fresh air. These gases commonly smell badly. They 

 come from decaying or other foul matters. Good air has 

 no odor, and it is safe to follow our noses when they 

 guide us out of any close place. But some of the very 

 worst air has no odor, and we must have other tests 

 than our noses. 



18, The causes of impure blood, just mentioned, are 

 apt to go together, and help each other. The person who 

 eats too much will not want to exercise, while he needs 

 the more to do so. 



Moderate use of alcohol often excites the appetite for 

 rich food to excess. The inordinate drinker is apt to lose 

 his appetite, and take too little food. Often he can digest 

 but little. 



QUESTIONS. 



SECTION I. 1, How does the body wear out ? 



4, How is it kept in repair ? Why must it finally die ? 



6, Why do we need sleep ? 



7, Why is sleepiness a safeguard? 



8, How can we know that we are not wearing out, when working 

 very hard ? 



9, How much sleep does a grown person need ? 

 10, Is sleep the only rest ? 



SECTION II. 1, From what materials is the waste of the body 

 repaired? What is the most important? 



2, How do we take in oxygen? How do we take in food and 

 water ? How are these distributed through the body ? 



3, What does the blood carry, besides the materials for repair? 



SECTION III. 1, What is blood? What are blood-globules? 

 What is their size? What proportion of the blood do they make? 



