414 MOVEMENTS 



The presence of cilia has been demonstrated on the following sur- 

 faces : The respiratory passages, including the nasal fossae, the pituitary 

 membrane, the summit of the larynx, the bronchial tubes, the superior 

 surface of the velum palati and the Eustachian tubes ; the sinuses about 

 the head ; the lachrymal sac and the internal surface of the eyelids ; 

 the genital passages of the female, from the middle of the neck of the 

 uterus to the fimbriated extremities of the Fallopian tubes ; some of the 

 seminal passages ; the ventricles of the brain and some unimportant sit- 

 uations. In these parts, on each cell of conoidal epithelium are six to 

 twelve processes, about 2TTiTo ^ an ^ nc ^ ( x ^) * n thickness at their base, 

 and ^Q^Q- to ^-^ of an inch (5 to 6 /-t) in length. Between the cilia and 

 the substance of the cell, there usually is a thin transparent disk. The 

 appearance of the cilia is represented in Fig. 80. When seen in situ, 

 they appear regularly disposed over the surface, are of nearly equal 

 length and are slightly inclined in the direction of the opening of the 

 cavity lined by the membrane. 



When the ciliary movements are seen in a large number of cells, the 

 appearance is well illustrated by the comparison by Henle to the undula- 

 tions of a field of wheat agitated by the wind. In watching this move- 

 ment, it usually is seen to gradually diminish in rapidity, until what at 

 first appeared simply as currents, produced by movements too rapid to 

 be studied in detail, are revealed as distinct undulations, in which the 

 action of individual cilia may be studied. Several kinds of movement 

 have been described, but the most common is a bending of the cilia, 

 simultaneously or in regular succession, in one direction, followed by an 

 undulating return to the perpendicular. The other movements, such as 

 the infundibuliform, in which the point describes a circle around the 

 base, the pendulum-movement etc., are not common and are unim- 

 portant. 



The combined action of the cilia on the surface of a mucous mem- 

 brane, moving as they do in one direction, is to produce currents of 

 considerable power. This may be illustrated under the microscope by 

 covering the surface with a liquid holding little solid particles in suspen- 

 sion, when the granules are tossed from one portion of the field to 

 another with considerable force. It is not difficult, indeed, to measure 

 in this way the rapidity of the ciliary currents. In the frog it has been 

 estimated at ^ J-Q to TFF ^ an ^ nc ^ (100 to 140 /-i) per second, the num- 

 ber of vibratile movements being seventy-five to one hundred and fifty 

 per minute. In the fresh-water polyp the movements are more rapid, 

 being two hundred and fifty or three hundred per minute. There is no 

 reliable estimate of the rapidity of the ciliary currents in man, but they 

 probably are more active than in animals low in the scale. 



