DUST AND ITS DANGERS. 



39 



lin^d with these delicate hairs which are called 

 cilia. 



Now, these myriads of cilia, year in and year 

 out, day and night, while life lasts, are con- 

 stantly swinging their free ends back and forth, 

 bending as they recover, and then with a quick 



L 



FIG. 3. CILIATED CELLS FROM THE LARGE AIR-TUBES OF THE 

 HUMAN LUNGS, SEEN FROM THE SIDE. HIGHLY MAGNIFIED. 



snap forward so that any small object which 

 lodges on the walls of the larger air-tubes 

 since all the cilia act in rhythm is swept up- 

 wards toward the mouth, away from the peril- 

 ously delicate and sensitive lungs. 



The movement of these cilia is less vigorous 

 when the body is quiet, as in sleep, increasing 

 m rap<sh-Uj ond -fa-rce when Ifre ia^y )$ *cf i^e 



. 



