RESPIRATION 



191 



stantly moict 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 



Flo. 51. SECTION OF THE MOUTII AND THROAT 



A, The Tongue 



B, The Uvula 



C, Vocal Cord 

 E, Epiglottis 

 L, Larynx 



N, Trachea 

 O, lEsophagus 



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 produca 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 



