CILIARY MOTION. 



33 



Cilia. 



Cell-body. 



"-.Nucleus. 



FIG. 23. Ciliated cells from the bron- 

 chus of the dog, the left cell with two 

 nuclei ; X 600 (Bohm and Davidoff ). 



to the free surface of the cells. The cells which bear the cilia are 

 usually of the columnar variety. 



Ciliated epithelium covers the mucous membrane of the respir- 

 atory tract, which begins with the nose and ends in the alveoli of 

 the lung, with the following exceptions : The olfactory membrane 

 (that part of the mucous mem- 

 brane of the nose to which the 

 olfactory nerves are distributed), 

 the lower part of the pharynx, 

 the surface of the vocal cords, 

 the ultimate bronchi, and the 

 lung-alveoli. It covers also 

 the mucous membrane of the 

 tympanum, except the roof, 

 promontory, ossicles, and mem- 

 brana tympani, where the epi- 

 thelium is of the pavement 

 variety and non-ciliated. Cil- 

 iated epithelium occurs also in 

 the Eustachian tube, the Fal- 

 lopian tube, the cavity of the 

 body of the uterus and of the upper two-thirds of the cervix, the 

 vasa eiferentia and coni vasculosi of the testicle, the ventricles 

 of the brain, and the central canal of the spinal cord. Some 

 observers have seen ciliated epithelium in the convoluted tubules 

 of the kidney. 



Ciliary Motion. Cilia are composed of protoplasm, and, 

 like other protoplasm, have the power of motion ; but ciliary 

 motion, though in some respects like that known as ameboid, is in 

 other respects quite different. Instead of being slow, it is very 

 rapid ten times and more a second so much so that when active, 

 the individual cilia which produce it are indistinguishable. It has 

 been likened to the movement of a field of wheat over which a 

 breeze is passing. The effect of this movement is to produce 

 a current always in one direction, and this current is often of con- 

 siderable physiologic importance : thus it is to its influence that 

 the ovum is carried down the Fallopian tube in the human female ; 

 and, according to some authors, were it not for the ciliated epithe- 

 lium in this canal the ovum would not find its way into the tube, 

 but at the time it escapes from the ovary would fall into the 

 peritoneal cavity and degenerate. 



Various explanations have been given to account for ciliary 

 motion. One which seems reasonable is that it is due to the same 

 cause which produces ameboid movement, namely, the flow of the 

 hyaloplasm into and out of the spongioplasm. It is a well-known 

 fact that if cilia are severed from the cells of which they form 

 a part, this motion ceases, so that intimate connection with the 



