CILIARY MOTION. 511 



According to M. Donne, 1 cilia are seen only on the "true mucous 

 membranes" of his division, 2 or those that secrete an alkaline mucus. 

 They are never met with on the acid membranes, which are analogous 

 to the skin, and simple reflections of the cutaneous envelope. Hence, 

 they are not found in the mouth or vagina, but in the nasal and bron- 

 chial mucous membrane. 



The organs of ciliary motion are delicate transparent filaments, 

 varying in length, according to Purkinje and Valentin, from j^o 7 ? to 

 y^jg of an inch, and are generally thicker at the base than at the free 

 extremity. Their motion continues after death as long as the tissues 

 retain their contractility, and often much longer. Miiller 3 thus sums 

 up the present state of our knowledge in regard to the phenomenon: 

 That the ciliary motion of the mucous membranes is due to the action 

 of some unknown contractile tissue, which lies either in the substance 

 of the cilia or at their base, that this tissue resembles in contractility 

 the muscular and other contractile tissues of animals; that its pro- 

 perties so far agree with those of the muscular tissues at all events 

 with those of the involuntary muscles of the heart, and the vibratory 

 laminse of the lower Crustacea ; that the motions, which it produces, 

 continue without ceasing with an equable rhythm ; that its properties 

 agree also with those of the muscular tissue of the heart in its motions, 

 continuing long after the separation of the part from the rest of the 

 animal body ; that this tissue differs essentially, however, from muscle, 

 in the circumstance of its motions not being arrested by the local ap- 

 plication of narcotics; and lastly, that the ciliary motion presents 

 itself under conditions where it is not probable that a complicated 

 organization exists, namely, in the undeveloped embryos of polypiferous 

 animals. 



M. Donne* 4 regards the cilia as animalcules; resembling in many 

 respects the spermatozoids. They certainly resemble each other ; but 

 there is no sufficient reason to believe either of them animalcular. 



The production of currents by the ciliary motion is not easy of ex- 

 planation. Purkinje and Valentin ascribe them to the return of the 

 cilia from the bent to the erect state, which gives an impulse to the 

 fluid. The direction in which the cilia act is most commonly towards 

 the outlet of the canal on which they are placed; but, as Mr. Paget 5 

 has remarked, their special purpose is in many instances for example, 

 in the ventricles of the brain as uncertain as the power by which they 

 act. 



We shall have to refer to ciliary motion under other heads. 



1 Coursde Microscopie, p. 170, Paris, 1844. 



2 See Secretion of Mucus in vol. ii. of this work. 



3 Elements of Physiology, by Baly, P. iv. p. 866, Lond., 1838. 



4 Op. cit., p. 176. 6 Brit, and For. Med. Review, July, 1842, p. 264. 



