4 



The Mechanism of Ciliary Movement. 113 



in sea-water the gill is in an environment which may have a sub-normal 

 concentration of potassium. 



In contrast to the lateral cilia, the fronto-lateral, the frontal and the 

 terminal cilia beat normally for very long periods (more than 48 hours) in a 

 solution containing no potassium. 



This contrast is paralleled by the action of such a solution when perfused 

 through the heart of different molluscs. In the case of Pecten Mines (25) 

 showed that potassium could be omitted from the perfusion fluid without any 

 derangement of the heart beat ; on the other hand, the heart of the Octopus 

 gradually stops in such a solution (Kleefeld, 17), and can be revived on adding 

 potassium. 



If potassium is present in excess a similar contrast is found in its 

 effects on the different cilia. Until the concentration of potassium is raised 

 to about ten times the normal value, little or no effect is noticeable upon the 

 cilia, although there is a tendency for a rapid secretion of mucus of the 

 surface of the gill, which may clog the frontal and terminal cilia. Above this 

 concentration the fronto-lateral cilia are affected in a curious way — they pass 

 into a state of contraction which persists for a considerable period. At first 

 the tips of the cilia remain bent at the end of the recovery phase of the beat, 

 then a wave passes along a whole series of the cilia which accentuates this 

 bend to a marked degree ; this is followed by another wave in which one 

 cilium after another remains fixed in a completely contracted position (i.e., at 

 the end of the effective beat). In this position the cilia often exhibit a 

 curious quivering movement. 



There is thus a regular " staircase " effect — similar to that found in the case 

 of the heart. 



If the concentration of potassium has not been too strong, the cilia 

 recover on transference to normal sea- water after about 15 minutes. Even if 

 contraction of the fronto-lateral cilia is brought about by a solution in which 

 the whole of the NaCl in the Van't Hoff solution has been replaced by KC1, 

 it is noticeable that after about 45 minutes, the cilia begin to recover in the 

 original solution, the amplitude of the beat getting gradually larger until the 

 complete beat is resumed. The rate of the recovery in such a solution, or in 

 normal sea- water, is greatly hastened by the presence of alkali. 



In all solutions containing excess of KC1, the beat and rhythm of the 

 lateral cilia is well maintained and is often more rapid than in the normal 

 gill ; the frontal and terminal cilia are either unaffected or beat more rapidly 

 than normal. Here again the differential action of potassium on different 

 tissues is clearly illustrated. 



Lillie and Hober have both emphasized the maintenance of ciliary movement 



