356 Mr Gray, The Mechanism of Ciliary Movement 



some of the tension energy of the fibres is stored in the cihum as 

 a whole. The supply of the chemically active substance now ceases, 

 and that portion already located in the fibres diffuses away, so thac 

 the cihum flies forward by virtue of its stored potential energy. 



In order to test this hypothesis the first obvious hue of enquiry 

 is to locate the essential parts of the cihary mechanism. This prob- 

 lem cannot now be discussed at length: it may suffice to say that 

 the cihum is not of itself automatic ; when separated from the cell 

 it does not move. The essential portions of the mechanism lie 

 towards the free edge of the cell. The nucleus does not appear to 

 play an essential role. 



Owing to the small size of ciliated cells, it is impossible to 

 analyse the movement by such mechanical methods as are applic- 

 able to a muscle; ciliated cells have, however, one great advantage 

 in that each individual cell can be observed. Thus, when the ampli- 

 tude of the contraction of the heart is gradually abohshed, it is 

 impossible to say whether this is due to the partial reduction of 

 the contraction of all the cells, or to the total abolition of contraction 

 in some cells, while the amplitude of the others remains unaltered. 

 In the case of cilia this difficulty does not exist, as the beat of a 

 single cilium can be observed throughout the whole experiment. 



During the present work an attempt has been made to analyse 

 cihary movement by a determination of possible means whereby 

 the movement can be influenced or abolished in a reversible manner, 

 i.e. without serious derangement of the mechanism itself. 



1. The effect of acids and alkalis. 



As shown in a previous publication* cilia are extremely sensitive 

 to acids. A certain degree of acidity in the external medium causes 

 a cessation of movement. There is no reduction in the amplitude 

 of the beat: the speed of both the effective and recovery beats 

 becomes gradually slower, often with prolonged pauses at the end 

 of each stroke. Eventually the cilia come to rest at the end of the 

 effective stroke. Since there is no diminution in the actual amount 

 of contraction, we are forced to conclude that the ciha do not stop 

 because the actual contractile or elastic mechanisms are deranged 

 but because the rate at which the transformation of chemical into 

 potential energy is gradually reduced and finally ceases. Further, 

 the rate at which potential energy is converted into kinetic energy 

 is also reduced. This conclusion is confirmed by the study of cells 

 in which we know that the amount of convertible chemical energy 

 is small, viz., spermatozoa. The work of Cohnf has shown that in 



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

 t E. J. Cohn, Biological Bulletin, vol. 34, 1918, p. 167. 



