36 COMPARATIVE PHYSIOLOGY 



is complete antagonism between the sodium and calcium ions. 

 This is also true of potassium and calcium, but the critical 

 ratio is not the same. 



When amoebas are torn in water by Chamber's technique 

 the surface is rapidly repaired after outflow of some of the cell 

 contents. Slight tearing in NaCl or KCl prevents any repair 



M . . 



in solutions of — concentration. With weaker solutions 



13 

 repair takes place with increasing ease in NaCl as the dilution 



M M 



is increased. In solutions of > ^r CaCl2 or > — MgCl2 



repair does not occur ; the surface sets into a solid mass. 

 The antagonism between the monovalent and divalent ions is 



M M 



seen again in this process : in a solution of NaCl — . CaCl2 — 



or of KCl . CaClo — b z repair of a torn surface takes 



13 ^ 208 416 ^ 



place in the normal manner. 



Pantin (1925) has also investigated the relation of electrolytes 



to the velocity of amoeboid movement, and has obtained 



somewhat analogous results. The marine amoeba is destroyed 



in isotonic solutions of the chlorides of the four principal 



kations present in sea water {i.e. sodium, magnesium, potassium, 



and calcium). For actual movement to take place calcium 



must be present. The addition of a minute trace of calcium 



to a solution of sodium or potassium alone permits movement 



to continue for a short time. Movement can be prolonged 



indefinitely by increasing to a certain optimum value the 



proportion of calcium to sodium in a solution containing these 



two kations alone. In this relationship calcium can be 



replaced by strontium, but not by any other kation. In a 



mixture of sodium and calcium, sodium may be replaced by 



any alkali metal ; but it is found that the optimum ratio of 



calcium to monovalent ion with respect to the velocity of 



amoeboid movement differs for different alkali metals, increasing 



with the atomic weight of the latter. In the presence of a trace 



of calcium the addition of magnesium to a certain optimum 



