FORMATION OF THE TISSUES EPITHELIUM. 473 



have supposed. And experiment also shows this independence. If the abdominal aorta 

 be tied, the muscles of the lower extremities will be paralyzed in consequence of their 

 being deprived of their blood ; and on removing the ligature, and allowing the b'ood to 

 flow, the muscles will recover themselves. But a ciliated surface is not affected at all 

 in its movements, though the supply of blood to the subjacent tissues be completely cut 

 off. Again, hydrocyanic acid, opium, strychnine, belladonna, substances which exert a 

 powerful effect on the nervous system, produce no influence upon ciliary motion: in the 

 bodies of animals killed by these poisons, the phenomenon is still conspicuous; and even 

 the local application of them does not hinder it, provided the solutions do not injure the 

 epithelial texture. Shocks of electricity passed through the ciliated parts, do not affect 

 the movement. Lastly, the removal of the brain and spinal cord in Irogs, by which all 

 muscular movements are destroyed, does not stop the action of the cilia. This striking 

 fact may likewise be adduced to disprove the supposition, that these movements result 

 from the action of minute muscles; for, although muscles maybe excited to contract 

 without nerves, we have no instances in the higher animals in which they habitually act 

 without the interference of the nervous system; nor is it likely that a movement existing 

 over so extended a surface as that by the cilia, would, if effected by muscles, be inde- 

 pendent of nervous influence. 



Alterations of temperature affect the ciliary motion, owing, doubtless, to the physical 

 change they induce in the epithelial particles. In warm-blooded animals it ceases on a 

 reduction of the temperature below 43 F. In cold-blooded animals, however, it continues 

 even at 32. In all, a very high temperature effectually puts a stop to it. It is interest- 

 ing to notice, that all observers agree in stating, that blood is the best preservative of the 

 ciliary motion, but the blood of Vertebrata destroys it in the Invertebrata. Bile puts a 

 stop to it, very probably by reason of its thick and viscid nature, arid not from any chemi- 

 cal influence. 



This phenomenon exists most extensively in the animal kingdom. It has been found 

 in all the vertebrate classes; and in the Invertebrata likewise, with the exception of the 

 Crustacea, arachnida, and insects. It is the agent by which the remarkable rotation of 

 the embryo in the ova of Mollusca is effected; and it occurs on the surface of the ova of 

 polypes and sponges. The bodies of some of the Infusoria are covered with cilia, which 

 are apparently employed by them as organs of locomotion, and for the prehension of food 

 (fig. 107, 2, 5). 



In man, the ciliary motion has been ascertained to exist on several surfaces: 1. On 

 the surface of the* ventricles of the brain and on the choroid plexuses. So delicate are 

 the cells of epithelium here, that the slightest mechanical injury destroys them; it is, 

 therefore, very difficult to see the movement. Valentin states that its duration is consi- 

 derable in these parts, so that it may be seen in subjects used for dissection. 2. On the 

 mucous membrane of the nasal cavities, extending along the roof of the pharynx to its 

 posterior wall, on a level with the atlas, on the upper and posterior part of the soft palate, 

 and in the immediate neighbourhood of the Eustachian tube, extending through the tube 

 itself to the cavity of the tympanum. 3. On the membrane lining the sinuses of the 

 frontal bone, the sphenoid, and the superior maxillary. 4. On the inner surface of the 

 lachrymal sac and lachrymal canal. 5. On the membrane of the larynx, trachea, and 

 bronchial tubes. 6. On the lining membrane of the female organs of generation. It does 

 not exist in the vagina; but it may be traced from the lips of the os uteri, through its 

 cavity, and through the Fallopian tubes to their nmbriated margins. 



In nearly all these instances there appears to be a mechanical use for the ciliary move- 

 ment, namely, to promote the expulsion of the fluid secreted by the surfaces on which the 

 cilia exist. Wherever the direction of the motion has been ascertained, it is that which 

 would be favourable to such a purpose. In the bronchial tubes and trachea, the direction 

 of the motion is towards the larynx, so that the cilia may be regarded as agents of expec- 

 toration. In the nose of the rabbit, Dr. Sharpey observed the impulse to be directed for- 

 wards, and in the maxillary sinus it appeared to pass towards the back part of the cavity, 

 where its opening is situated. In the Fallopian tube, the direction is stated by Purkinje 

 and Valentin to be from the fimbriated extremity towards the vagina. It seems very 

 probable that ciliary motion exists in the kidney, at the narrow neck of each uriniferous 

 tube, as it passes off from the capsule of the Malpighian body. This has not been actu- 

 ally observed in the human subject. It was discovered, and has been frequently seen in 

 the frog.* The movement is here directed towards the uriniferous tube, and it doubtless 

 is destined to favour the flow of the aqueous portion of the secretion from the capsule of 

 the tube. 



In the inferior animals the cilia seem to answer a similar end to that in man. 'J hey 

 exist extensively on respiratory surfaces, and in connection with the generative organs; 



* Bowman, Phil. Trans., 1842. 

 40* 



