The Mechanism, of Ciliary Movement. 



117 



corresponding muscle cell. The cilium is essentially an elastic fibre in 

 communication with and dependent upon the protoplasm of the cell.* The 

 cilium is capable of storing potential energy (supplied to it from the cell) in 

 the form of tension, and of liberating this energy in the form of work. The 

 amount of tension developed depends on the existence of free water in the 

 cell. The rate at which the energy is stored and liberated by the cilium 

 depends upon the hydrogen ion concentration of the cell interior. Whereas 

 the rate of movement of the cilium depends almost completely upon the 

 concentration of hydrogen ions inside the cell, it is largely independent of 

 the presence of specific metallic ions (except in certain cases potassium) in 

 the external medium. 



A suggestion as to the way in which chemical activity within the cell may 

 lead to the development of a tension in a fibrous structure (in the presence 

 of water) is provided by the experiments of Fischer and Strietmann (9). 

 These authors have shown that, if a piece of catgut, suspended in water, 

 comes into contact with an acid, the fibre absorbs water and develops a 

 considerable tension. The same phenomenon occurs in the presence of an 

 alkali. In this experiment the essential conditions are : (i) the liberation of 

 a chemical (acid or alkali) on the surface of a fibre ; (ii) the presence of water. 

 These facts form the basis of an hypothesis of muscular actions, but they 

 can be applied with equal force to the ciliary mechanism. In the case of the 

 muscle fibre, the production of an acid (lactic acid) during stimulation has 

 been demonstrated. If the same fact be assumed to be true in the case of a 

 cilium, then many of the facts stated in this paper receive a reasonable 

 explanation. The rate at which lactic acid is produced from its carbohydrate 

 precursor depends upon the hydrogen ion concentration of the medium 

 (Kondo, 19). Hence, the rate at which chemical energy can be converted 

 into potential energy will also depend upon the hydrogen ion concentration 

 of the cell interior. It is therefore clear why the rate of the recovery stroke 

 of the cilia of Mytilus is affected by acids which enter the cell. By our 

 hypothesis, at the end of the recovery stroke the cilium possesses potential 

 energy, owing to the stress set up in its elastic structure by the tension of 

 those fibres at whose surface an acid is situated. This potential energy can 

 only be liberated by the relaxation of the fibres ; that is, by the removal of 

 the acid. The rate at which the acid is removed will depend upon the 

 degree of alkalinity of the surrounding cell contents. In other words, an 

 explanation is available for the effect of acids and alkalies on the rate of the 

 effective stroke of the cilium. 



* The truth of this statement can be seen by reference to most text-books of histology, 

 or to the work of Saguchi(29). 



VOL. XCI1I. — B. K 



