58 HUMAN PHYSIOLOGY 



Any small bodies which adhere to such surfaces are 

 accordingly carried along with the creeping film. Prog- 

 ress is slow, it may be only H inch in a minute, but it 

 is definite and sometimes a matter of importance. 



The effects of ciliary movement may be seen when the 

 esophagus of a frog is laid open and bits of chalk are 

 sprinkled upon the lining membrane. These will be 

 taken steadily toward the stomach. The cilia con- 

 tinue to be active long after the death of most other 

 tissues. This demonstration upon the frog is so com- 

 monly made that students need to be told that there are 



FIG. 9. A portion of ciliated epithelium as it might be seen under 

 the microscope if that instrument could give a perspective effect. 

 At the front the cells are sectioned, while above and receding we have 

 their ciliated surface. There is a suggestion of coordinated movement 

 in that the cilia in great numbers have a parallel direction but it is not 

 supposed that the order of the actual performance can be presented 

 to the eye. 



no cilia upon the lining of the esophagus in the mammal. 

 The cleansing of this passage which is accomplished by 

 the cilia in the frog is effected in ourselves by swallowing 

 saliva or water. 



Human beings do have cilia in the respiratory tract. 

 TJie lining of the nasal cavities is equipped in this way 

 and so is that of the lower passages leading from the 

 larynx to the depths of the lungs. Particles of dust, 

 including many germs, which settle upon these surfaces 

 are not allowed to remain where they fall but are at 

 once put in motion. In the bronchial tubes the move- 



