358 Mr Gray, The Mechanism of Ciliary Movement 



the fibre, and so the degree of tension set up in the fibres may 

 be due to the difference in the concentration of hydrogen ions at 

 the surface of the fibres and in some other part of the cell. 



On the other hand, it is possible that if the acidity of the whole 

 cell is raised to the value which normally only exists at the surface 

 of the fibres, there may be a breakdown in the whole colloidal 

 structure of the cell. 



2. The effect of metallic ions. 



It has already been shown* that an artificial solution containing 

 NaCl, KCl, MgCla, and CaClg whose Ph is about 7-8 forms a satis- 

 factory medium for ciliary activity. If a similar solution be prepared 

 in which KCl is omitted the different cilia on the gill react in 

 different ways. The frontal cilia and terminal cilia are practically 

 unafi:ected within two or three hours; the lateral ciha, however, 

 quickly stop. On adding KCl to the solution they rapidly recover. 

 Recovery can also be brought about by making the solution slightly 

 more alkaline. It is interesting to note that the lateral cilia beat 

 in a definite rhythm, and it is possible that potassium is necessary 

 for this rhythm. If the concentration of potassium be increased 

 above the normal value, the beat of these cilia is well maintained ] 

 even in solutions in which the whole of the NaCl is replaced by KCl ; 

 the frontal and terminal cilia are not appreciably affected; the 

 latero-frontal cilia however go into a state of prolonged contraction. 

 After some time they gradually recover. The effect of potassium 

 on the latero-frontals is antagonised by alkali. Further work is 

 required for an elucidation of these facts, but it is interesting to 

 note the different effects of potassium on different types of ciha. 



If an artificial solution be prepared which contains all the normal 

 constituents with the exception of Ca--, all the cilia come to rest 

 within 1t2-2 hours. If Ca-- is added as soon as the ciha have ceased 

 to beat, complete recovery takes place : if, however, the addition of 

 Ca-- is delayed for some time, the recovery is much less perfect, 

 the rate of beat is slow and there is often a marked pause at the 

 end of the recovery stroke. After stoppage in the absence of Ca-, 

 rapid and complete recovery takes place on the addition of alkah, 

 even when Ca-- continues to be absent. It is noticeable that the 

 effect of the absence of Ca-- upon cilia is similar to the action of 

 such solutions upon the heart. It is not clear whether the effect of 

 alkali mobilises further stores of Ca--, or whether the absence of 

 Ca-- causes a reduction in the alkalinity of the cell interior. Minesf 

 concluded that in the absence of Ca-- the heart ceases to beat 

 because the actual contractile mechanism is deranged, while the 



* J. Gray, Quart. Journ. Micros. Scietice, vol. 64, 1920, p. 345. 

 t G. R. Mines, Journ. of Phys. vol. 46, 1913, p. 188. 



