CILIAEY MOTIOX. 49 



water. The undulating movement may be beautifully seen on the gills 

 of a mussel. The undulations, with some exceptions, seem always to 

 travel in the same direction on the same parts. The impulsion, also, 

 which the cilia communicate to the fluids or other matters in contact 

 with them, maintains a constant direction ; unless in certain of the 

 infusoria, in which the motion is often variable and arbitrary in direc- 

 tion, and has even been supposed to be voluntary. Thus in the wind- 

 pipe of mammalia, the mucus is conveyed upwards towards the larynx, 

 and, if a portion of the membrane be detached, matters will still be 

 conveyed along the surface of the separated fi-agment in the same 

 direction relatively to that surface, as before its separation. 



The persistence of the ciliary motion for some time after death, and 

 the regularity with which it goes on in parts separated from the rest of 

 the body, sufficiently prove that, with the possible exceptions alluded 

 to, it is not under the influence of the will of the animal nor dependent 

 for its production on the nervous centres, and it does not appear to bo 

 influenced in any way by stimulation or sudden destruction of these 

 centres. The time which it continues after death or separation differs 

 in different kinds of animals, and is also materially influenced by tem- 

 perature and by the nature of the fluid in contact with the surface. In 

 warm-blooded animals the period varies from two or three hours to two 

 days, or even more ; being longer in summer than in the cold of winter. 

 In frogs the motion may continue four or five days after the destruction 

 of the brain ; and it has been seen in the gullet of the tortoise fifteen 

 days after decapitation, continuing seven days after the muscles had 

 ceased to be irritable. 



With tlie view of throwing further light on the nature of this 

 remarkable kind of motion, experiments liave been made to ascertain 

 the effect produced on it by different physical, chemical, and medicinal 

 agents ; but, so far as these experiments have gone, it would seem that, 

 with the exception of moderate heat and cold, alkaline solutions, chlo- 

 roform vapour, and perhaps some other narcotics, these agents affect 

 the action of the cilia only m so far as they act destructively on their 

 tissue. 



The effect of change of temperature is different in warm and in cold-blooded 

 animals. In the former the motion is stopped by a cold of 4.S° F., whereas in the 

 frog and river-mussel it goes on unimpaired at 32° F. E. H. Weber made the 

 interesting observation that, in ciliated epithelium particles detached fi-om the 

 human nasal membrane, the motion which has become languid or quiescent 

 from the cold may be revived by wannth, such as that of the breath, and this 

 several times in succession. A moderately elevated temperature, say 100° F., does 

 not affect the motion in cold-blooded animals ; but, of course, a heat considerably 

 higher than this and such as to alter the tissue, would put an end to it in all 

 cases. Electric shocks, unless they cause abrasion of the ciliated siu-face (which. 

 is sometimes the case), produce no ■visible effect ; and the same is tme of 

 galvanic cuiTents. Fresh water an-ests the motion in marine moUusca and in 

 other salt-water animals ; but it evidently acts by destroying both the fonn and 

 substance of the cilia, which in these cases are adapted to a different medium. 

 Most of the common acid and salme solutions, when concentrated, an-est the 

 action of the cilia instantaneously in all animals ; but dilution delays this effect, 

 and when earned faither, j^revents it altogether ; and hence it is, probably, due 

 to a chemical alteration of the tissue. Yu-chow has observed that a solution of 

 either potash or soda will revive the movement of cilia after it has ceased. Nar- 

 cotic substances, such as hydrocyanic acid, salts of morphia and strychnia, opium 

 and belladonna, are said by Piu-kinje and Valentin to have no effect, though the 

 VOL, II. E 



