36 HANDBOOK OF PHYSIOLOGY. 



to the eye of the observer is very similar to that produced by waves in a 

 field of corn, or swiftly running and rippling water, and the result of 

 their movement is to produce a continuous current in a definite direc- 

 tion, and this direction is invariably the same on the same surface, 

 being always, in the case of a cavity, toward its external orifice. 



Ciliary Motion. Ciliary, which is closely allied to amoeboid and 

 muscular motion, is alike independent of the will, of the direct 

 influence of the nervous system, and of muscular contraction. It may 

 continue for several hours after death or removal from the body, pro- 

 vided the portion of tissue under examination be kept moist. Its inde- 

 pendence of the nervous system is shown also in its occurrence in 

 the lowest invertebrate 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 applica- 

 tion of narcotics, such as morphia, opium, and belladonna, to the 

 ciliary surface, or of electricity through it. The vapor of chloroform 

 arrests the motion; but it is renewed on the discontinuance of the 

 application. The movement ceases when the cilia are deprived of 

 oxygen, although it may continue for n time in the absence of free 

 oxygen, but is revived on the admission of this gas. Carbonic acid 

 stops the movement. The contact of various substances, e.g., bile, strong 

 acids, and alkalies, will stop the motion altogether; but this seems to 

 depend chiefly on destruction of the delicate substance of which the 

 cilia are composed. Temperatures above 45 C. and below C. stop 

 the movement, whereas moderate heat and dilute alkalies are favorable 

 to the action and revive the movement after temporary cessation. The 

 exact explanation of ciliary movement is not known; whatever may be 

 the exact cause, however, at any rate the movement must depend upon 

 some changes going on in the cell to which the cilia are attached, as 

 when the latter are cut off from the cell the movement ceases, and when 

 severed so that a portion of the cilia are left attached to the cell, the 

 attached and not the severed portions continue the movement. Some 

 authorities consider it due to actual contraction of the cilia themselves; 

 others assert that it is caused by movements in the cell protoplasm acting 

 upon the rootlets of the cilia. Schiifer suggests a very plausible ex- 

 planation, viz., that a cilium is either a curved hollow extension of the 

 cell, which is filled by hyaloplasm and invested by a delicate membrane, 

 or else a straight one whose investing membrane is thicker (or otherwise 

 less extensible) along one side than along the other. In either case a 

 rhythmic flowing of the hyaloplasm into and out of the cilium would 

 cause its alternate flexion and extension. 



As a special subdivision of ciliary action may be mentioned the motion 

 of spermatozoa, which may be regarded as cells with a single cilium. 



