RESPIRATION 



181 



stantly moist condition. This membrane has cells of a 

 peculiar kind upon its outer surface. If examined under a 

 powerful microscope, we may see, even for a considerable time 

 after their removal from the body, that these cells have minute 

 hair-like processes in motion, which wave like a field of grain 



FIG. 51. SECTION OF THE MOUTH AND THROAT 



A, The Tongue 



B, The Uvula 



C, Vocal Cord 

 E, Epiglottis 

 L, Larynx 



N, Trachea 

 O, (Esophagus 



under the influence of a breeze (Fig. 52). This is a truly 

 beautiful sight ; and since it is found that these little cilia, as 

 they are called, always produce currents in one direction 

 from within outward it is - probable that they serve a useful 

 purpose in catching and carrying away from the lungs dust 



