50 CILIA. 



fii-st-named agent lias certainly appeared to us to an-est the motion in the river- 

 mussel. In confinnation of an observation of Lister * we find that exposui'e 

 for a few moments to the vapour of chlorafoim arrests ciliary action, and that 

 the motion revives again if the application of the vapour is discontinued. 



Bile stops the action of the cilia, while blood prolongs it in vertebrated animals ; 

 but the blood or sei-um of the vertebrata has quite an opposite effect on the cilia 

 of invertebrate animals, an-esting then- motion almost instantaneously. 



Whatever views maybe entertained concerning the nature and source 

 of the power by which the cilia act, it must be borne in mind that each 

 ciliated cell is individually endowed with the faculty of producing 

 motion, and that it possesses in itself whatever organic apparatus and 

 whatever physical or vital property may be necessary for that end ; 

 for single epithelium cells are seen to exhibit the phenomenon long 

 after they have been completely insulated. 



It seems not unreasonable to consider the ciliary motion as a manifestation 

 of that jiroperty on which the more conspicuous motions of animals are known 

 to depend, namely, vital contractility ; and this view has at least the advantage 

 of refen-ing the phenomenon to the operation of a vital property ah-eady 

 recognised as a som-ce of moving power in the animal body. But, a^uming this 

 view to be sound, so far as regards the natm-e of the motile propei-ty brought 

 into play, it affords no explanation of the cause by which the contractility is 

 excited and the cilia maintained in constant action. 



It is true that nothing resembling a muscidar apparatus in the ordinary sense 

 of the tei-m, has been shown to be connected -Rdth the cilia, nor is it necessary to 

 suppose the existence of any such ; for it must be rememljered that, while the 

 organic substance on which vital contractility depends is probably uniformly the 

 same in composition, it does not eveiywhere assume the same fonn and texture. 

 The anatomical characters of human voluntary muscle differ widely from those 

 of most involuntary muscular structui'es, and still more from the contractile 

 tissues of some of the lowest invertebrate animals, although the movements must 

 in all these cases be refen-ed to the same principle. Tlie heart of the embiyo 

 beats while yet but a mass of cells, united, to all appearance, by amorphous 

 matter, in which no fibres are seen ; yet no one would doubt that its motions 

 depend then on the same property as at a later period, when its structui-e is fully 

 developed. 



In its persistence after systemic death and in parts separated from the rest of 

 the body, the ciliary motion agrees with the motion of certain muscular organs, 

 as the heart, for example ; and the agi'eement extends even to the regular or 

 rhjiihmic character of the motion in these circumstances. It is true, the one 

 endui-es much longer than the other ; biit the difference appeai-s to be one 

 only of degi'ee, for similar differences are known to prevail among muscles 

 themselves. No one, for instance, doubts that the aui-icle of the heart is mus- 

 cular, because it beats longer after death than the ventricle : nor. because a frog"s 

 heart continues to act a much longer time than a quadi-uped's. is it infen-ed that 

 its motion depends on a power of a different natui-e. And the view here taken 

 of the nature of the ciliary motion derives strength from the consideration that 

 the phenomenon lasts longest in cold-blooded animals, in which vital contractility 

 also is of longest endm-ance. In the effects of heat and cold, as far as observed, 

 there is also an agi-eement betAveen the movement of cilia and that of muscular 

 parts ; while, on the other hand, it must be allowed that electricity does not 

 appear to excite their activity. Thvi effects of narcotics afford little room for 

 inference, seeing that our knowledge of then- local action on muscular in-itability 

 is by no means exact ; but in one instance, at least, an agent, chloroform 

 vapour, which stops the action of the freshly excised heart of a frog, arrests also 



* Phil. Trans. 1858, p. 690, where will he fouud other valuable observations on the 

 effect of external agents on ciliary action. 



