100 FACTORS AFFECTING CILIARY ACTIVITY 



the more marked is the reversal response, both in its longer 

 duration and in its lovv^er threshold level. An accumulation of 

 Ca++ in the cell seems to be necessary if the cilia are to show 

 reversal, although Ueda (1956) has shown that a maintained 

 reversal is evoked in Opalina injected with Ca++ precipitants, so 

 that reversal is evoked by a diminution of the free Ca++ in the cell. 



Some polyvalent ions have been found to increase the beating 

 activity of the membranelles of Stentor in experiments on animals 

 cultured in a medium containing only K+, Na+, Ca++, Cl~, 



HCO3- and PO4 (Sleigh, 1956a). The effects on the frequency 



of beat of Stentor membranelles of the addition of magnesium 

 chloride and aluminium chloride to this medium are shown in 

 Fig. 25. A maximum increase in frequency of beat of about 20 

 per cent was recorded at a magnesium chloride concentration of 

 • 125 m mol, the addition of which increases the total molarity of 

 the medium by less than 10 per cent, but markedly increases the 

 ratio of divalent cations to monovalent cations (about 4:150 in the 

 normal medium). Aluminium chloride increases the rate of beat 

 at even lower concentations. It is interesting that these increases 

 in the rate of beat were not accompanied by any change in the 

 metachronal wave velocity. In this report it was suggested that 

 the effects of Mg++ and A1+++ on the beating activity were the 

 result of changes in protoplasmic viscosity caused by the action 

 of the ions on the ionisation of protoplasmic colloids, since 

 Heilbrunn (1923) had found that the addition of magnesium 

 chloride reduced the viscosity of Stentor protoplasm. It is also 

 possible that Mg++ may affect the chemical parts of the contrac- 

 tion and energy liberation processes, in which it is known to 

 participate, as well as interfering with the normal balance between 

 polyvalent and monovalent cations. 



The effect of cation concentrations on metazoan cilia has been 

 mainly studied on Mytilus gill cilia, where the effects on different 

 groups of cilia are not always the same. Among the monovalent 

 cations, K+ and Na+ are the most abundant, and both can be 

 varied over a wide range without affecting the beat of the frontal 

 cilia. In balanced solutions of calcium chloride, magnesium 

 chloride and the chloride of a single monovalent cation, Gray 

 (1922b) found that the frontal cilia were stopped in Li+ and 

 accelerated in NH4+ and K+, especially the latter, while in Na"*" 



