IONS 95 



and stopped completely at about 20 per cent sea water (Tomita, 

 1934a). Roots (1955) found that in two species of oligochaete 

 worms the nephridiostome cilia were accelerated by dilution of 

 the medium and slowed in hypertonic media, but these effects 

 were only temporary. Large changes in the osmotic pressure 

 of the medium caused some damage and serious long-term 

 effects. 



The effects of osmotic pressure on the change in beat direction 

 of Opalina reported by Naitoh (1959) follow a rather similar 

 pattern. In a hypertonic medium the animal shrank, but the 

 direction of beat remained unchanged and the cilia continued to 

 beat until the membrane was considerably deformed. On return 

 to the normal medium, however, the beating quickly started again, 

 but in the reversed direction, only to return to normal when the 

 body had finished swelling. In a hypotonic medium, the swelling 

 was accompanied by a reversal of the direction of beat, while the 

 shrinkage on return to the normal medium had no effect on the 

 direction of beat. Naitoh was able to show that these changes 

 were due to hypotonicity and not to ion deficiency, and he deduced 

 that the stretching of the membrane was the factor causing the 

 change in the direction of beat of the cilia. Thus he could change 

 the beat direction by stretching the cell membranes either by 

 injecting liquids into the cell or by the use of two microneedles 

 which were moved apart; in both cases the beat returned to normal 

 on removal of the stimulus. 



It is well known that the osmotic pressure of the medium 

 affects the motility of spermatozoa, and here again it is found that 

 hypotonic media have a greater inhibitory effect than hypertonic 

 media. Emmens (1948) found that the effect of hypotonic media 

 on rabbit spermatozoa was increased at acid pH and reduced in 

 alkaline media. 



7. Ions and Ciliary Activity 



A reasonably steady balance of most ions is found in natural 

 environments, but it is often useful to vary ionic concentrations 

 experimentally in order to investigate the part they play in 

 physiological processes. The concentration of hydrogen ions, 

 on the other hand, varies quite widely in nature, and is found to 

 have important effects on ciliary activity. 



