30 CELLULAR 



cells were placed in it, thus bringing the inner 

 and outer surfaces of the protoplasm in contact 

 with identical solutions (since the sap can be 

 extracted without being altered). Most of these 

 cells lived but a short time (as a rule less than 

 a week), while under the same conditions in sea 

 water the majority live for several months. 

 This does not seem to be due to bacterial action 

 for the cells died promptly in sap which had 

 been boiled and filtered. 



Normally there is considerable difference be- 

 tween the acidity of the sap and the sea water 

 (the pH values of sap and sea water are 5.8 and 

 8.2 respectively). When cells are placed in their 

 own sap this difference is abolished. Is this re- 

 sponsible for their rapid death? To answer this 

 question the acidity of the external sap was 

 varied j the results showed that acidity is not the 

 primary factor involved although cells die 

 much more quickly at pH 5.8 than at 8.2. 



The important factor might conceivably be 

 the maintenance of differences in electric poten- 

 tial between the inside and outside of the proto- 

 plasmic layer but this does not seem to be the 



