86 FACTORS AFFECTING CILIARY ACTIVITY 



viscous medium, while the metachronal co-ordination rate is 

 unchanged because the conduction process is internal and in- 

 dependent of the frequency. As the viscosity increases, the move- 

 ments of the viscous medium caused by the beating of any cilium 

 have an increased effect on the movement of neighbouring cilia, 

 and at about 3 • 5 cP the movement of one cilium begins to assist 

 the movement of its neighbours sufficiently for the frequency to 

 be increased. The direct communication of viscous drag from 

 one cilium to the next is faster than the internal conduction 

 process, and triggers off the contraction of the next cilium before 

 the conducted impulse arrives, so that the metachronal wave 

 velocity is increased. The higher the viscosity, the greater the 

 viscous drag and the faster the metachronal wave velocity. The 

 increases of both frequency and metachronal wave velocity are 

 limited by the progressive decrease of amplitude, for with a small 

 amplitude of beat less viscous drag is developed, neighbouring 

 cilia assist each other less and eventually the metachronal waves 

 break down. 



A recent report that the metachronal wavelength and the 

 metachronal wave velocity of Opalina cilia was decreased by an 

 increase in viscosity (Potter, 1960) is very interesting, and has 

 been confirmed by the author. The metachronal relationships of 

 these cilia (p. 183) are quite different from those of Stentor 

 membranelles, so that we need not necessarily expect the effect 

 of viscosity to be the same; nevertheless, it is worthy of further 

 experimentation. 



4. Hydrostatic Pressure and Ciliary Activity 



Many physiological processes have been studied under increased 

 hydrostatic pressure, and valuable information has thereby been 

 obtained. Our knowledge of the effects of pressure on ciliary 

 activity is scanty. Regnard (1884) and Certes (1884) both found 

 that pressures of 500-600 atm (6800-8000 Ib/in^) stopped the 

 ciliary movement of various infusoria. Under increased pressure, 

 Paramecium shows decreased speed of movement and sometimes 

 complete stoppage, but Ebbecke (1935b) found that these changes 

 were immediately and completely reversed on the release of 

 pressure. Ebbecke's (1935a) experiments on Beroe swimming 

 plates gave rather different results — their movements stop at about 



