CILIARY ACTIVITY 



27 



Circumstantial evidence also pointing to the conclusion that 

 the acid enters the cells is gained from a study of the effects of 

 removal of calcium. Lillie (1900) originally showed that the 

 toxic effect of pure sodium salts on ciliary movement, as on 

 muscular contraction and on irritability in nerve, is prevented 

 by the presence of the alkaline earth metals. In the case of 

 the ciliated cell either magnesium or calcium will serve in 

 adequate proportions to maintain the normal semipermeability 

 of the cell membrane, but magnesium must be present to 

 ensure recovery (according to Gray) after exposure to a solution 



60 6 4 6 8 7-2 7-6 6 B '^ 

 Hydrogen Ion Concentration P^ 



Fig. 9. — Relation of hydrogen ion concentration to ciliary movement 



(after Gray). 



containing no divalent ions. On the other hand, if calcium 

 is replaced by an equivalent amount of magnesium, cessation 

 of ciHary movement is brought about unless the pH. is kept 

 well above absolute neutrality. 



In other words, the cell is more susceptible to the action of 

 hydrogen ions if the calcium ions, which confer upon the 

 membrane its normal semipermeability, are removed. More 

 direct evidence that the acid enters the cell is obtained by 

 intra vitam staining with an indicator, such as neutral red. 

 Before drawing conclusions from these data one other fact 

 may be mentioned. At the critical point the cilia are brought 



