VISCOSITY 



85 



than normal, the wavelength is increased by over 100 per cent in 

 some cases. Under these conditions of high viscosity the meta- 

 chronal waves and the frequency are less stable than usual, and 

 the amplitude is progressively reduced with increase of viscosity 

 until the beats become a mere flicker. Metachronal waves cease 

 and eventually all beating stops at about 10 cP. 



♦120- 



3*0 >0 7*0 



VISCOSITY IN CENTIPOISES 



Fig. 20. The effect of viscosity on metachronal wave velocity 



and frequency of beat of Stentor membranelles. Each value 



plotted is the mean of many observations, the vertical lines 



showing 95 per cent confidence limits (from Sleigh, 1961). 



The explanation given for these results is closely bound up with 

 theories of the mechanism of metachronal co-ordination of these 

 cilia which is considered in detail later (p. 184). At low viscosities 

 the ciliary beat is slowed by the mechanical resistance of the 



