462 MOVEMENTS VOICE AND SPEECH. 



to the perpendicular. The other movements, such as the infundibuliform, 

 in which the point describes a circle around the base, the pendulum-move- 

 ment etc., are not common and are unimportant. 



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

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

 erable power. This may be illustrated under the microscope by covering the 

 surface with a liquid holding little, solid particles in suspension ; Avhen the 

 granules are tossed from one portion of the field to another, with consid- 

 erable 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 ^ to -^ of an 

 inch (100 to 140 //,) per second, the number 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 cur- 

 rents 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 spermato- 

 zoids, seem to be independent of nervous influence, and they are affected only 

 by local conditions. They will continue, under favorable circumstances, for 

 more than twenty-four hours after death, and they can be seen in cells entire- 

 ly 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 feebly alkaline solutions. 

 There seems to be no possibility of explaining the movement except by a 

 simple 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 movements, it is sufficient to refer to the physi- 

 ology 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 gen- 

 erally and in the genital passages of the female, the currents are of consid- 

 erable 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 mem- 

 branes. These are distinct from muscular movements, and are not even to 

 be classed with the movements produced by the resiliency of muscular tissue, 

 in which muscular tonicity is more or less involved. Movements of this kind 

 consist simply in the return of movable parts to a certain position after they 

 have been displaced by muscular action, and in the reaction of tubes after 

 forcible distention, as in the walls of the large arteries. 



Elastic Tissue. Most anatomists adopt the division of the elements 

 of elastic tissue into three varieties. This division relates to the size of 

 the fibres ; and all varieties are found to possess essentially the same chem- 

 ical composition and general properties. On account of the yellow color of 

 this tissue, presenting, as it does, a strong contrast to the white, glistening 



