THE BODY TEMPLE 51 



If some cruel fellow should catch that frog and cut 

 off his hind legs to eat, you might dissect his body, and 

 in doing so you would find inside of it two good sized 

 air-bags, connected with the frog's mouth by a little 

 tube. Before the frog goes under water, he swallows 

 air sufficient to fill these bags ; then, after being under 

 water awhile, he comes up to exchange it for a fresh 

 supply. 



We have in our bodies air-bags, called lungs, simi- 

 lar to those of the frog, only much more complicated 

 in structure. A frog is obliged to swallow air because 

 he has no ribs; but we are enabled, by the arrange- 

 ment of the ribs forming the chest, to expand the lungs, 

 and thus suck in the air through the mouth or nose. 

 A frog only needs to exchange the air in its lungs once 

 in ten or fifteen minutes, and may under some circum- 

 stances go without breathing for a much longer time. 

 But our lungs require that the air which they contain 

 should be changed eighteen or twenty times a minute 

 when we are quiet, and twice as fast when we run or 

 engage in any violent exercise. 



The use of the lungs is to remove certain impurities 

 from the blood. To facilitate this work, they are lined 

 with a delicate membrane which, if spread out, would 

 cover a surface of more than two thousand square feet, 

 or about eighty square rods. Underneath this mem- 

 brane, an amount of blood equal to the entire quan- 

 tity contained in the body, passes every minute for 

 purification, giving off certain poisonous elements, 

 and taking up the life-giving oxygen, which it car- 

 ries to all the tissues, thus giving them life and 

 activity. 



A Plant that Eats Flies. —Did you ever see a 

 plant eat?— Probably not. Most plants eat in such a 



