PHTSIOLOGT 31 



case, as measurements show that practically no 

 such difference exists. 



The primary factor seems to be a lack of cer- 

 tain elements in the external medium which are 

 needed to make a "balanced solution." It is 

 evident that the sap is not a balanced solution in 

 the ordinary sense and this raises the question 

 whether balanced solutions are in general neces- 

 sary for the interior of the cell. 



There is some ground for believing that the 

 maintenance of differences between the interior 

 and exterior of the cell is essential for carrying 

 on vital processes in general. 



The fact that juices from the interior of the 

 cell may be toxic when applied to the exterior 

 may find a parallel in certain observations on 

 animals. Many investigators believe that when 

 tissues are burned or crushed, toxic substances 

 are set free. It may be that these substances are 

 due to reactions which never take place except 

 as the result of injury, but it is possible that 

 some of these substances are normally present in 

 the interior of the cell, in which case we should 

 have an analogy to what is observed in Valonia. 



