IONS 



97 



abolished if the acid is able to penetrate the whole cell, and thus 

 only the weak acids are fully eiTective. Gray (1928) has suggested 

 that the stoppage of cilia of molluscs like Mytilus by carbonic acid 

 is important in the life of these animals because the accumulation 

 of CO2 in the closed shell inhibits the ciliary movement and 

 reduces the oxygen consumption. Nomura (1932) denies this and 

 suggests that the stoppage of ciUa in an enclosed space results 

 from oxygen lack, since the amount of CO2 is not sufficient for 

 stoppage. It is quite possible that neither explanation is correct, 

 and that the stoppage of the beat of at least some gill cilia is a 

 nervous reflex action (see p. 121). 



All cilia do not give the same response at the same pH, and it 

 seems that there is some adaption to the normal pH of the sur- 

 roundings. Thus, Tomita (1934b) reported that the gill cilia of 



Table 8. The relation between the minimum pH at which cilia 



FROM different CILIATED EPITHELIA OF Mya WILL FUNCTION AND THE 

 NORMAL pH of THEIR SURROUNDINGS (FrOM YoNGE, 1925) 



Ostrea circiimpincta are more resistant to pH than those of 

 Mytilus. The cilia of different internal regions of the body of Mya 

 normally function at diflPerent pH, and Yonge (1925) found that a 

 diflFerent pH was required to stop the movement of cilia of differ- 

 ent origins; these findings are shown in Table 8. 



Cilia of Paramecium cause maximum forward movement at 

 pH between 5-1 and 6-3 (Chase and Glaser, 1930; Dryl, 1961); 

 activity falls away quickly in more acid media and slowly in 

 alkaline media. The activity of spermatozoa varies with pH in 

 much the same way. In a study of rabbit spermatozoa, Emmens 

 (1947) found that sperm are immobilized and quickly die at pH 



