524 MOVEMENTS. 



studied in detached cells, in the human subject, by introducing a feather into the nose, by 

 which a few cells may be removed with the mucus and can be observed in the same way. 

 This demonstration serves to show the similarity between the movements in man and in 

 the lower orders of animals. When the movements are seen in a large number of cells 

 in situ, the appearance is very graphically illustrated by the apt comparison of Henle to 

 the undulations of a field of wheat agitated by the wind. In watching this movement, 

 it is usually seen to gradually diminish in rapidity, until what at first appeared 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. Sev- 

 eral 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 unimportant. 



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 

 illustrated 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 measure in this 

 way the rapidity of the ciliary currents. In the frog it has been estimated at from -gfa 

 to y^ of an inch per second, the number of vibratile movements being from seventy-five 

 to one hundred and fifty per minute. In the fresh- water polyp the movements are more 

 rapid, being from two hundred and fifty to three hundred per minute. There is no reli- 

 able estimate of the rapidity of the ciliary currents in man, but they are probably more 

 active than in animals low in the scale. 



The movements of cilia, like those observed in fully-developed spermatozoids, seem 

 to be entirely independent of nervous influence, and they are affected only by purely local 

 conditions. They will continue, under favorable circumstances, for more than twenty- 

 four hours after death and can be seen in cells entirely detached from the body when 

 they are moistened with proper fluids. When the cells are moistened with pure water, 

 the activity of the movement is at first increased ; but it soon disappears as the cells 

 become swollen. Acids arrest the movement, but it may be excited by feeble alkaline 

 solutions. All abnormal conditions have a tendency either to retard or to abridge the 

 duration of the ciliary motion. It is true that, when the movement is becoming feeble, 

 it may be temporarily restored by very dilute alkaline solutions, but the ordinary stimuli, 

 such as are capable of exciting muscular contraction, are without effect. Purkinje and 

 Valentin, Sharpey, and others, have attempted to excite the movements of cilia by gal- 

 vanic stimulus, but without success. Anesthetics and narcotics, which have such a 

 decided effect upon muscular action, have no influence upon the cilia. 



It is useless to follow the speculations that have been advanced to account for the move- 

 ment of cilia. There is no muscular structure in the cilia, no connection with the nervous 

 system, and there seems to be no possibility of explaining the movement except by a bare 

 statement of the fact that the cilia have the property of moving in a certain way so long 

 as they are under normal conditions. As regards the physiological uses of these move- 

 ments, it is sufficient to refer to the physiology of the parts in which cilia are found, 

 where the peculiarities of their action are considered more in detail. In the lungs and 

 the air-passages generally and in the genital passages of the female, the currents are of 

 considerable importance ; but it is difficult to imagine the use of these movements in 

 certain other situations, as the ventricles of the brain. 



Movements due to Elasticity. There are certain important movements in the body 

 that are due simply to the action of elastic ligaments or membranes. These are entirely 

 distinct from muscular movements, and are not even to be classed with the movements 



