Mr Gray, The Mechanism of Ciliary Movement 357 



such cells the cessation of movement in an acid solution involves 

 no wastage of energy : the acid simply prevents the chemical energy 

 being converted into kinetic energy. 



It is important to notice that the efficiency of acids to cause 

 cessation of movement depends upon the ease with which they 

 penetrate the cell surface, so we may conclude that the liberation 

 of chemical energy into potential energy takes place inside the 

 cell, and not at its surface. 



The effect of all moderate strengths of acid {i.e. those strengths 

 which rapidly stop movement but do not kill the cell) is entirely 

 reversible by means of alkalis. Again, we find that the efficiency 

 of alkahs depends upon the ease with which they penetrate into 

 the cell, e.g. ammonia is much more efficient than the strong alkalis. 

 Within fairly wide limits the rate of ciliary movement depends 

 upon the alkalinity of some area with the cell — from about Ph5 to 

 PglO there is a progressive increase in the rate of beat. 



The reduction in the rate of transformation of chemical energy 

 into potential energy, by an increase in the acidity of the cell 

 interior, is in accord with Kondo's* investigations on the rate of 

 production of lactic acid from muscle extract. The production of 

 lactic acid from muscle extract is a self-limited reaction which 

 is checked by the formation of the lactic acid — or by another acid 

 in the medium. The fact that the effective beat of a cilium is 

 slowed when the cell interior is more acid than normal is clearly 

 explicable if we assume that the liberation of the potential energy 

 into kinetic energy is dependent upon the rate at which an acid, 

 like lactic acid, diffuses away from some special structure or fibre 

 — the more acid the cell or medium the slower will the potential 

 energy be Hberated. 



It is clear that the observed facts so far described, place no 

 obstacle in the way of accepting our provisional hypothesis. There 

 is, however, one point which should be mentioned. If potential 

 energy can be stored in the cilium by the liberation of lactic acid 

 at the surface of certain fibres, then one would expect that if lactic 

 acid or any other acid is used as an experimental means of stopping 

 ciliary action, the fibres should remain in the shortened condition, 

 and not in the relaxed state. If the concentration of the experi- 

 mental acid is raised above the minimum value to cause stoppage 

 of movement, it is true that the cilia move away from the fully 

 relaxed position, but they never approach the end of the recovery 

 beat. The same phenomenon occurs with muscle fibres which are 

 rendered inexcitable by acid. As pointed out by Minesj, however, 

 the shortening of the muscle fibre (or the distortion of a ciUum) is 

 brought about by a local concentration of acid at the surface of 



* K. Kondo, Biochem. Zeit. vol. 45, 1912, p. 63. 

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



