452 FUNCTIONS OF CILIA. 



in sea water ; or the hard palate of a frog, newly killed, may be scraped and the scraping ex- 

 amined in | p.c. salt solution. On analysing the movement, all the cilia will be observed to 

 execute a regular, periodic, to and fro rhythmical movement in a plane usually vertical to the 

 surface of the cells, the direction of the movement being parallel to the long axis of the organ. 

 The appearance presented by the movements of the cilia is sometimes described as a lashing 

 movement, or like a field of corn moved by the wind. Each vibration of a cilium consists of a 

 rapid forward movement or flexion, the tip moving more than the base, and a slower backward 

 movement, the cilium again straightening itself. The forward movement is about twice as rapid 

 as the backward movement. The amplitude of the movement varies according to the kind of 

 cell and other conditions, being less when the cells are about to die, but it is the same for all the 

 cilia attached to one cell, and is seldom more than 20 to 50. There is a certain periodicity 

 in their movement in the frog they contract about 12 times per second. The result of the 

 rapid forward movement is that the surrounding fluid, and any particles it may contain, are 

 moved in the direction in which the cilia bend. All the cilia of adjoining cells do not move at 

 once, but in regular succession, the movement travelling from one cell to the other, but how 

 this co-ordination is brought about we do not know. At least it is quite independent of the 

 nervous system, as ciliary movement goes on, in isolated cells, and in man it has been observed 

 in the trachea two days after death. Conditions for Movement. In order that ciliary move- 

 ment may go on, it is essential that (1) the cilia be connected with part of a cell; (2) moisture ; 

 (3) oxygen be present ; and (4) the temperature be within certain limits.] 



[A ciliated epithelial cell is a good example of the physiological division of labour. It is 

 derived from a cell which originally held motor, automatic, and nutritive functions all com- 

 bined in one mass of protoplasm, but in the fully developed cell, the nutritive and regulative 

 functions are confined to the protoplasm, while the cilia* alone are contractile. If the cilia 

 be separated from the cell, they no longer move. If, however, a cell be divided so that part of 

 it remains attached to the cilia, the latter still move. The nucleus is not essential for this' act. 

 It would seem, therefore, that though the cilia are contractile, the motor impulse probably 

 proceeds from the cell. Each cell can regulate its own nutrition, for during life they resist the 

 entrance of certain coloured fluids.] 



[Effect of Reagents. Gentle heat accelerates the number and intensity of the movements, 

 cold retards them. A temperature of 45 C. causes coagulation of their proteids, makes them 

 permanently rigid, and kills them, just in the same way as it acts on muscle, causing heat- 

 stiffening ( 295, 1). Weak alkalies may cause them to contract after their movement is 

 arrested or nearly so ( Virchoiv), and any current of fluid in fact may do so. Lister showed 

 that the vapour of ether and chloroform arrests the movements as long as the narcosis lasts, 

 but if the vapour be not applied for too long a time, the cilia may begin to move again. The 

 prolonged action of the vapour kills them. As yet we do not know any specific poison for 

 cilia atropin, veratrin, and curara acting like other substances with the same endosmotic 

 equivalent (Engelmann).] 



[Functions of Cilia. The moving cilia propel fluids or particles along the 

 passages which they line. By carrying secretions along the tubes which they line 

 towards where these tubes open on the surface, they aid in excretion. In the re- 

 spiratory passages, they carry outwards along the bronchi and trachea, the mucus 

 formed by the mucous glands in these regions. When the mucus reaches the 

 larynx it is either swallowed or coughed up. That the cilia carry particles upwards 

 in a spiral direction in the trachea has been proved by actual laryngoscopic investi- 

 gation, and also by excising a trachea and sprinkling a coloured powder on its 

 mucous membrane, when the coloured particles (Berlin blue or charcoal) are slowly 

 carried towards the upper end of the trachea. In bronchitis the ciliated epithelium 

 is shed, and hence the mucus tends to accumulate in the bronchi. They remove 

 mucus from cavities accessory to the nose, and from the tympanum, while the ova 

 are carried partly by their agency from the ovary along the Fallopian tube to the 

 uterus. In some of the lower animals they act as organs of locomotion, and in 

 others as adjuvants to respiration, by creating currents of water in the region of the 

 organs of respiration.] 



[The Force of Ciliary Movement. Wyman and Bowditch found that the amount of work 

 that can be done by cilia is very considerable. The work was estimated by the weight which 

 a measured surface of the mucous membrane of the frog's hard palate was able to carry up an 

 inclined plane of a definite slope in a given time.] 



[Pigment-cells belong to the group of contractile tissues, and are well developed in the frog, 

 and many other animals where their characters have been carefully studied. They are generally- 

 regarded as comparable to branched connective-tissue corpuscles, loaded with pigmented granules 



