LUNGS, DUST, AND TOBACCO SMOKE 143 



Do this faithfully every morning, and do it whenever 

 you think about it during the day. The breastbone is 

 not hard when you are young, and if you are careful 

 to hold the chest up and breathe as you should the 

 bones will have a fine curved shape, and in the end you 

 will have a big, healthy, splendid chest and lungs. 



You know what sort of air you ought to breathe, and 

 you know about oxygen and carbon dioxid. There is 

 also dust in the air, which is very injurious to the lungs. 

 They cannot always save themselves from this, though 

 they do a good deal at it by a wonderful 

 arrangement which they have. 



On the inside of the largest tubes of 

 the lungs and inside the nose there are 

 thousands and thousands of little threads ClLIA READY FOR 

 called cilia. These cilia are like the tip 

 ends of the very finest cobweb silk, and they are mov- 

 ing all the time like tiny paddles. They are busy day 

 and night, through winter and through summer, for 

 their duty is to keep dust and microbes from getting 

 into the lungs. 



They are the air cleaners of the tubes, just as certain 

 men are the street cleaners of the city. When there is 

 dust in the air they paddle hard in such a way as to 

 drive it out of the lung tubes and out of the nose. They 

 manage very well most of the time ; still, when the lungs 

 belong to a man who not only lives in the dust all day 



