CHAPTER XV. 



CAUSES AND PHENOMENA OF MOTION. 



IN" the animal body, motion is produced in these several ways: (1.) 

 The oscillatory or vibratory movement of Cilia. (2.) Amoeboid and certain 

 Molecu lar movements. (3.) The contraction of Muscular fibre. 



I. CILIARY MOTION. 



Ciliary, which is closely allied to amoeboid and muscular motion (p. 8, 

 Vol. I.), consists in the incessant vibration of fine, pellucid processes, about 

 -g-^ of an inch long, termed cilia (Figs. 260, 261,) situated on the free 

 extremities of the cells of epithelium covering certain surfaces of the body. 



The distribution and structure of ciliary epithelium and the micro- 

 scopic appearances of cilia in motion have been already described (pp. 

 25, 26, Vol. I.). 



Ciliary motion is alike independent of the will, of the direct influ- 

 ence of the nervous system, and of muscular contraction. It continues 

 for several hours after death, or removal from the body, provided the 



FIG. 260. 



FIG. 261. 



FIG. 260. Spheroidal ciliated cells from the mouth of the frog; magnified 300 diameters. 

 (Sharpey.) 



FIG. 261. Columnar ciliated cells from the human nasal membrane: magnified 300 diameters. 

 (Sharpey.) 



portion of tissue under examination be kept moist. Its independence of 

 the nervous system is shown also in its occurrence in the lowest inverte- 

 brate animals apparently unprovided with anything analogous to a nervous 

 system, in its persistence in animals killed by prussic acid, by narcotic or 

 other poisons, and after the direct application of narcotics to the ciliary sur- 



