Chapter 39

lighted candle if shut up in a small, close place? to a mouse? Why is air so necessary for a burning candle and for animals? How is the heat of our bodies produced? Name the principal organs of breathing. Describe each. How do we use the lungs in breathing? How much air will a man's lungs hold? How much air do we use with each breath? What poisonous substance does the air which we breathe out contain? Will a candle burn in air which has been breathed? What happens to animals placed in such air? What change takes place in the blood as it passes through the lungs? How do plants purify the air?