CILIARY MOTION. 



455 



movement. The contact of various substances will stop the 

 motion altogether ; but this seems to depend chiefly on destruc- 

 tion of the delicate substance of which the cilia are composed. 



FIG. 153. 



FIG. 154. 



FIG. 153. Spheroidal ciliated cells from the mouth of the frog; magnified 300 

 diameters (Sharpey). 



FIG. 154. Columnar ciliated epithelium cells from the human nasal membrane ; 

 magnified 300 diameters (Sharpey). 



Little or nothing is known with certainty regarding the na- 

 ture of ciliary action. As Dr. Sharpey observes, however, it 

 is a special manifestation of a similar property to that by 

 which the other motions of animals are effected, namely, by 

 what we term vital contractility. The fact of the more evident 

 movements of the larger animals being effected by a structure 

 apparently different from that of cilia, is no argument against 

 such a supposition. For, if we consider the matter, it will be 

 plain that our prejudices against admitting a relationship to 

 exist between the two structures, muscles and cilia, rests on no 

 definite ground ; and for the simple reason, that we know so 

 little of the manner of production of movement in either case. 

 The mere difference of structure is not an argument in point ; 

 neither is the presence or absence of nerves. The movements 

 of both muscles and cilia are manifestations of force, by cer- 

 tain special structures, which we call respectively muscles and 

 cilia. We know nothing more about the means by which the 

 manifestation is effected by one of these structures than by the 

 other ; and the mere fact that one has nerves and the other 

 has not, is no more argument against cilia having what we call 

 a vital power of contraction, than the presence or absence of 

 stripes from voluntary or involuntary muscles respectively, is 

 an argument for or against the contraction of one of them 

 being vital and the other not so. Inasmuch then as cilia are 

 found in living structures only, and inasmuch as they are a 

 means whereby force is transformed (see Chap. II), their pe- 

 culiar properties have as much right to be invested with the 

 term vital as have those of muscular fibres. The term may be 



