Mr Gray, The Mechanism of Ciliary Movement 353 



Consider a simple strip of steel wire ABC attached at one end C 

 (Fig. 1 ). If a stress is applied to the wire so as to distort it to A^B^C, 

 then it is clear that in passing from the position of rest ABC to its 

 new position A^B^C, a considerable part of the energy used to disturb 

 the wire is stored in the wire, in other words when in the position 

 A^B^C the strip of wire possesses a definite amount of potential 

 energy. If we wish to make the wire do work in the direction from 

 u4 to ^1, it is obvious that such a mechanism would be extremely 

 inefficient since the w^hole of the potential energy taken up by the 

 wire itself would be unavailable for work. Consider now the same 

 wire distorted to abC. Again potential energy is stored. On releasing 

 the wire the whole of this energy is set free and is available for work. 



Heidenhain and numerous other workers have regarded cilia 

 as comparable to the wire which performs work in moving from 

 ^ to ^^. We therefore reach the paradoxical conclusion that cilia 

 perform a surprising amount of work*, and yet are exceedingly 

 inefficient machines. 



Let us now consider the actual movement of the frontal or 

 terminal cilia on the gills of Mytilus. 



Under normal conditions the rate of beat of these cilia is so 

 great, that it is only possible to observe the movement in detail 

 when the rate of beat is reduced by the addition of some viscous 

 but non-toxic substance {e.g. gum arable) to the external medium. 



During the forward or effective beat (Fig. 2) the cilium behaves as 



* Bowditch calculated that each cell of the mucous membrane of the Frog is 

 capable of lifting its own weight to a height of 14 feet in I min. 



