STUrCTURE OF CILIATED EPITHELIUM. 



47 



The fact of the conveyance of fluids and other matters along the ciliated 

 surface, as well as the direction in which they are impelled, may also be 

 made manifest by immersing the membrane in fluid, and dropping on 

 it some finely pulverised substance (such as charcoal in fine powder), 

 which will be'^ slowly luit steadily carried along in a constant and deter- 

 minate direction ; and this may be seen with the naked eye, or with the 

 aid of a lens of low power. 



The ciliary motion of the human mucous membrane is beautifully 

 seen on the surface of recently extracted nasal polypi ; and single 

 ciliated particles, with their cilia still in motion, are sometimes sepa- 

 rated accidentally from mucous surfaces in the living body, and may be 

 discovered in the discharged mucus ; or they may even be purposely 

 detached by gentle abrasion. But the extent and limits of the ciliated 

 epithelium of the human body have been determined chiefly from its 

 anatomical characters. 



Cilia have now been shown to exist in almost every class of animals, 

 from the highest to the lowest. The immediate purpose which they 

 serve is, to impel matter, generally more or less fluid, along the surfaces 

 on which they are attached ; or, to propel through a liquid medium the 

 ciliated bodies of minute animals, or other small objects on the surface 

 of which cilia are present ; as is the case with many infusorial animal- 

 cules, in which the cilia serve as organs of locomotion like the fins of 

 larger aquatic animals, and as happens, too, in the ova of many verte- 

 brate as well as invertebrate animals, where the yelk revolves in its 

 surrounding fluid by the aid of cilia on its surface. In many of the 

 lower tribes of aquatic animals, the cilia acquire a high degree of 

 importance : producing the flow of water over the surface of their 

 organs of respiration, indis- 

 pensable to the exercise of that Fig. 24. 

 function ; enabling the animals 

 to seize their prey, or swallow 

 their food, and performing 

 various other offices of greater 

 or less importance in their 

 econom3\ In man, and the 

 warm-blooded animals, their 

 use is apparently to impel 

 secreted fluids or other mat- 

 ters along the ciliated surface, 

 as, for example, the mucus of 

 the windpipe and nasal sinus- 

 es, which they carry towards 

 the outlet of these cavities. 



Structure. — The cells of 

 the ciliated epithelium (fig. 

 24) contain clear oval nu- 

 clei ; their protoplasm is 

 commonly granular, but the 

 free border of the cell from 

 which the cilia appear to spring 

 presents a bright appearance 

 (fig. 21). They have most 

 generally an elongated form, like the particles of the columnar 



Fig. 24. — Ciliated Epithelium Cells from 

 Trachea of Cat ; magnified about 600 

 diameters (Klein). 



