ELECTRIC CURRENTS 89 



immediate decrease in frequency, there was a further progressive 

 decrease which was not immediately reversible; this increased 

 with increase in time of exposure to high pressure, and was more 

 rapid at higher pressures. 



In observations on the effects of hydrostatic pressure on the 

 activity of a wide variety of flagellates and ciliates, Kitching 

 (1957) again found a diflFerence in response in different animals. 

 The movement of flagella or cilia of most of the organisms was 

 reduced at high pressures, and such movement usually stopped 

 after short exposure to pressures of 8000 to 14,000 Ib/in^; visible 

 structural damage was found to occur at about the same pressure. 

 An exception was found in the case of Epistylis plicatilis where 

 pressures of the order of 1000 to 3000 Ib/in^ caused an increase 

 in the rate of ciliary beat; higher pressures caused reduction of 

 ciliary movement and eventually stoppage. Increased pressure 

 was also found to affect the behaviour of many protozoa, for while 

 some organisms, e.g. Euplotes, showed increased activity at 

 moderate pressures (2000 to 4000 Ib/in^), others, e.g. Stylonychia^ 

 showed reduced activity. The ability to reverse and to perform 

 avoiding reactions was lost in Spirostomum at pressures above 

 about 4000 Ib/in^, and the ability of Stylonychia to perform 

 normal controlled movements was lost at somewhat higher 

 pressures. It is evident that systems of ciliary control are affected 

 by these high pressures, and that effects on the contraction 

 mechanism are not a complete answer to the problem. 



It is impossible to determine at present the reason for the 

 differences between the results obtained using different material. 

 Further work should prove valuable, especially in cases where 

 the contraction cycle of the cilia can be studied. 



5. Electric Currents and Ciliary Activity 



At about the turn of the century several workers experimented 

 on the effects of electric currents on cihated protozoa ; experiments 

 of this type on Paramecium have been reviewed by Wichterman 

 (1953), and may be summarized as follows. When swimming 

 paramecia are subjected to a weak direct current flowing between 

 two electrodes in the surrounding medium, the animals will turn 

 towards the cathode and swim towards it. If the current strength 

 is increased more animals respond and swim rapidly towards the 



