CILIATED EPITHELIUM. lix 



generally columnar, bear at their free extremities little hair-like pro- 

 cesses, which are agitated incessantly during life, and for some time after 

 death, with a lashing or vibrating motion. These minute and delicate 

 moving organs are named cilia. They have uo\v been discovered to 

 exist very extensively throughout the animal kingdom ; and the move- 

 ments which they produce are subservient to very varied purposes in the 

 animal economy. 



In the human body the ciliated epithelium occurs in the following parts, 

 viz. : 1. On the mucous membrane of the air passages and its pro- 

 longations. It commences at a little distance within the nostrils, covers 

 the membrane of the nose and of the adjoining bony sinuses, and extends 

 up into the nasal duct and lachrymal sac. From the nose it spreads back- 

 wards a certain way on the upper surface of the soft palate, and over the 

 upper or nasal region of the pharynx ; thence along the Eustachian tube 

 and lining membrane of the tympanum, of which it covers the greater part. 

 The lower part of the pharynx is covered by scaly epithelium as already 

 mentioned ; but the ciliated epithelium begins again in the larynx a little 

 above the glottis, and continues throughout the trachea and the bronchial 

 tubes in the lungs to their smallest ramifications. 2. On the mucous lining 

 of the uterus, commencing at the middle of the cervix and extending along 

 the Fallopian tubes, even to the peritoneal surface of the latter at their 

 ninbriated extremities. 3. Lining the vasa efferentia, coni vasculosi, and 

 first part of the excretory duct of the testicle. 4. To a large extent on 

 the parietes of the ventricles of the brain, and throughout the central canal 

 of the spinal cord. 



In other mammiferous animals, as far as examined, cilia have been found 

 in nearly the same parts. To see them in motion, a portion of ciliated 

 mucous membrane may be taken from the body of a recently killed quad- 

 ruped. The piece of membrane is to be folded with its free or ciliated 

 surface outwards, placed on a slip of glass, with a little weak salt water or 

 serum of blood, and covered with a bit of thin glass or mica. When it is 

 now viewed with a magnifying power of 200 diameters or upwards, a very 

 obvious agitation will be perceived on the edge of the fold, and this 

 appearance is caused by the moving cilia with which the surface of the 

 membrane is covered. Being set close together, and moving simultaneously 

 or in quick succession, the cilia, when in brisk action, give rise to the 

 appearance of a blight transparent fringe along the fold of the membrane, 

 agitated by such a rapid and incessant motion, that the single threads which 

 compose it cannot be perceived. The motion here meant, is that of the 

 cilia themselves ; but they also set in motion the adjoining fluid, driving it 

 along the ciliated surface, as is indicated by the agitation of any little 

 particles that may accidentally float in it. 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 but steadily carried 

 along in a constant and determinate 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 parti- 

 cles, with their cilia still in motion, are sometimes separated accidentally 

 from mucous surfaces in the living body, and may be discovered in the dis- 

 charged mucus ; or they may even be purposely detached by gentle abrasion. 



