PHTSIOLOGT 35 



sodium. Erythrocytes are of special interest. In 

 some cases they contain little or no sodium and 

 there is reason to believe that the large amount 

 of potassium which is present exists in solution 

 as an inorganic salt. On the other hand there are 

 species whose erythrocytes contain mostly so- 

 dium with very little potassium. 



It is therefore apparent that we are not war- 

 ranted in concluding that potassium invariably 

 predominates over sodium in the sap of living 

 cells. 



It may be noted that by adding ammonium 

 chloride to the sea water it is possible to substi- 

 tute ammonium to a certain extent for the so- 

 dium and potassium of the sap without appar- 

 ently injuring the cell. 



Another interesting problem is suggested by 

 the fact that the dissimilarity in composition of 

 the two Valonias bring about a marked difference 

 in their behavior in that V. fnacrofhysa sinks in 

 sea water while V . ventricosa floats. It may be 

 said in this connection that it would seem that 

 the flotation of living cells may be brought about 



