440 ' MOVEMENTS. 



fifty diameters, the currents produced in the liquid will be 

 strikingly exhibited. The movements may be studied in de- 

 tached cells, in the human subject, by introducing a feather 

 into the nose, when a few cells will be removed with the 

 mucus, and can be observed in the same way. 1 This demon- 

 stration serves to show the similarity between the movements 

 in man and in the lower orders of animals. When the move- 

 ments are seen in a large number of cells in situ, the ap- 

 pearance is very graphically illustrated by the apt comparison 

 of Henle to the undulations of a field of wheat agitated by 

 the wind. 2 In watching this movement, it is usually seen 

 to gradually diminish in rapidity, until what at first ap- 

 peared simply as a current, produced by movements too 

 rapid to be studied in detail, becomes revealed as distinct 

 undulations, in which the action of individual cilia can be 

 readily studied. Purkinje and Valentin describe several 

 kinds of movement, 3 but the most common is a bending of 

 the cilia, simultaneously or in regular succession, in one di- 

 rection, followed by an undulating return to the perpendicu- 

 lar. The other movements, such as the infundibuliform, in 

 which the point describes a circle around the base, the pen- 

 dulum-movement, etc., are not common, and are unimpor- 

 tant. 



The combined action of the cilia upon the surface of a 

 mucous membrane, moving as they do in one direction, is to 

 produce currents of considerable power. This may be illus- 

 trated under the microscope by covering the surface with a 

 liquid holding little solid particles in suspension. In this case 

 the granules are tossed from one portion of the field to another 

 with considerable force. It is not difficult, indeed, to meas- 

 ure in this way the rapidity of the ciliary currents. In the 

 frog it has been estimated at from ^-g- to T ^ of an inch per 

 second, the number of vibratile movements being from 



1 BECLARB, op. cit., p. 497. 



2 HENLE, Traite tfanatomie generate^ Paris, 1843, tome i., p. 263. 



3 Loc. cit. 



