94 FACTORS AFFECTING CILIARY ACTIVITY 



and swims towards it; negatively charged colonies swim to the 

 cathode. Mast suggested that an ion shift within the colony when 

 it is an electric field could cause changes in potential and perme- 

 ability, and increase in permeability causes decreased flagellar 

 activity. 



Electric currents are not without effect on ciliated tissues of 

 metazoa, although this has been rarely studied. The beating of 

 comb -plates of the ctenophore Beroe may be inhibited for \ 

 minute or more by passing a current of 1 to 2 mA/sq. cm through 

 the animal from the oral (anode) to the aboral ends (Gothlin, 

 1929). Similarly, Segerdahl (1922) found that the laterofrontal 

 cilia of the gill filaments of Anodonta were accelerated by a 

 current of about 0-1 mA/sq. mm, while the lateral cilia are 

 inhibited by this current, especially when the current is passing 

 from the base of the ciliated cells towards their tips. She has also 

 found that these lateral cilia were excited to a more rapid 

 beat by passing a current of about 1 mA/sq. mm through the gill; 

 after this current is switched off, ciliary movement may be 

 inhibited in cells where the current had been passing from the 

 surface to the base. It is interesting to compare these results on 

 the lateral cilia with those of Naitoh on Opalina. 



It is evident, then, that electric currents sometimes increase the 

 movement of cilia, sometimes reverse it, and sometimes inhibit it, 

 depending on the organism and the conditions. Attempts have 

 also been made to detect the presence of electrical changes in 

 ciliated tissues, and to correlate these with the ciliary activity. 

 The change of membrane potential with reversed ciliary beat in 

 Opalina has already been mentioned, and other electrical changes 

 are also thought to take place. 



6. Osmotic Pressure and Ciliary Activity 



A slight increase in the osmotic pressure of the medium around 

 the gill filaments of Mytilus may cause a slight reduction in the 

 amplitude of beat, but no change in the rate of beat (Gray, 

 1922a). With a large increase in osmotic pressure all movement 

 stops, irrespective of the nature of the osmotic agent. In hypo- 

 tonic media, the gills of Ostrea circiimpincta showed slightly 

 increased mechanical activity at concentrations between 50 and 

 100 per cent sea water ; below 50 per cent the activity was decreased 



