606 



CILIA. 



raucous membranes.* Dr. Hope's and M. Bil- 

 lard's cases were destitute of villi, and the 

 latter expresses a doubt whether it ever takes 

 place. Our own observations decidedly incline 

 us to the same opinion. 



Like all adventitious organic products, cica- 

 trices are very readily irritated and are de- 

 stroyed by ulceration with amazing rapidity. 

 A few days and even a few hours are sometimes 

 sufficient to undo the restorative labours of 

 many months; but this destruction is often su- 

 perficial, and then the after-healing is as rapid 

 as the previous ulceration. 



M. Dupuytrenf informs us that the cicatrix 

 resulting from an entire destruction of the skin 

 is not liable to be affected by many exanthe- 

 matous diseases, such as scarlet fever, measles, 

 and small-pox; it remains pale in the midst of 

 the inflammation and eruption which covers 

 the neighbouring parts. The contrary takes 

 place only in superficial cicatrices, under which 

 some layers of the original cutis exist, and 

 which participate in the properties as well as 

 in the inflammatory tendencies of the rest of 

 the skin. 



In conclusion we may state, that it appears, 

 from the previous considerations, that in the 

 repairing of the injuries in question, beautiful 

 as is the process and useful as are the results, 

 yet nature's great object does not consist so 

 much in an endeavour to restore the lost struc- 

 ture in all its functions and perfections of 

 organization, as merely to produce a covering 

 for those parts which remain uninjured, to act 

 as a defence to them from external irritations 

 and injuries, and possessed therefore only of 

 such a degree of vitality and of such properties 

 of structure as shall be sufficient for its own 

 preservation and repair. 



(A. T. S. Dodd.) 



CILIA,J (in anatomy, Fr. Cils; Germ. 

 Wimperhaare.) This term is used to desig- 

 nate a peculiar sort of moving organs, re- 

 sembling small hairs, which are visible with 

 the microscope in many animals. These organs 

 are found on parts of the body which are 

 habitually in contact with water or other more 

 or less fluid matters, and produce motion in 

 these fluids, impelling them along the surface 

 of the parts. The currents or other motions 

 thus produced serve various purposes in the 

 economy of the animals in which they occur. 

 In other circumstances the cilia serve as 

 organs of locomotion, some aquatic animals 

 propelling themselves through the water by 

 their means. 



Cilia have now been ascertained to exist in 

 a great many invertebrated and in all verte- 

 brated animals, except Fishes ; having been 

 very recently discovered by Purkinje and Va- 

 lentin on the respiratory and uterine mucous 

 membranes of Mammalia, Birds, and Reptiles. 



The terms " vibratory motion " and " ciliary 

 motion" have been employed to express the 



* Med. Chir. Rev. vol. x. p. 324. 



t Op. cit. tome ii. p. 48. 



i For another signification of this term, see the 

 articles EYE and LACHRYMAL APPARATUS. 



Fishes are no longer an exception : see note' 

 at page 632. 



appearance produced by the moving cilia; 

 the latter is here preferred, but it is used to 

 express the whole phenomenon as well as the 

 mere motion of the cilia. 



A considerable space has been allotted to 

 the present article, more perhaps than its re- 

 lative importance may seem to demand, chiefly 

 for the reason that, with one exception, no 

 attempt has been hitherto made to collect and 

 describe under appropriate heads, the facts 

 known on the subject. The exception alluded 

 to is a work by Purkinje and Valentin,* which 

 appeared while this article was in progress, and 

 which contains not only an account of their own 

 discovery, but a history of all preceding obser- 

 vations. But the manner of treating the sub- 

 ject in the work alluded to is for the most part 

 so different from that which is here followed, 

 that its publication has not seemed to warrant 

 any material abridgement of the following 

 article, which, on the contrary, it has increased 

 by affording much new and important matter, 

 as will be acknowledged in its proper place. 

 Another ground on which indulgence may be 

 claimed for details which are, perhaps, greater 

 than may seem commensurate with the impor- 

 tance of the subject, is that many of the facts 

 are here described for the first time, and it was 

 felt desirable to state them in their full extent, 

 which could not be done intelligibly without 

 considerable length of description. 



The article is divided into two parts ; the 

 first comprehends the particular facts, or an 

 account of the phenomena as they occur in the 

 different tribes of animals considered in Zoo- 

 logical order, with the history of their dis- 

 covery; the second part consists of general 

 deductions from the first, and also treats of the 

 structure and mode of action of the cilia in 

 general. This method has been adopted as 

 appearing on the whole best suited to the pre- 

 sent state of knowledge on the subject. 



PART I. 



1. Infusoria. Cilia exist very extensively 

 in the different tribes of Infusory Animalcules ; 

 indeed they constitute the principal organs of 

 motion in these small animals. When a drop 

 of water containing Infusoria is brought under 

 the microscope, these creatures are seen swim- 

 ming rapidly through it in various directions ; 

 and as they move along, small particles of 

 foreign matter which happen to lie near their 

 path are thrown into agitation, obviously in- 

 dicating the existence of currents in the neigh- 

 bouring water. When the animals remain 

 steady in one place, these currents become 

 much more distinct, setting in particular di- 

 rections, and causing the small particles to run 

 in a stream to and from the animal. If the 

 magnifying power be sufficiently strong, small 

 transparent filaments will be distinguished, 

 projecting from the surface of the animalcules 

 and moving in a very rapid manner. These 

 are the cilia ; they serve like fins or paddles 

 to carry on the animal in its progression through 

 the water, and when it is stationary, they impel 

 the water in a current along the surface, which 



* De phenomeno motus vibratorii, &c. 4to. 

 Wratisl. 1835. 



