112 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



2. Evidence has been given of the correctness of Loeb's 

 suggestion that the antagonistic action of one salt on 

 another is due to the fact that the one hinders the other 

 from entering the cell. 



3. The facts brought to light are not at variance with 

 the view that the plasmatic membrane is proteid rather 

 than lipoid. 



4. The usual plasmolytic methods of determining os- 

 motic pressure by salt solutions are at fault. 



5. The confusion between true and false plasmolysis has 

 often led to error. 



These conclusions have been tested by the electrical 

 method also, in which the resistance of living tissue is 

 measured. 



THE ELECTRICAL CONDUCTIVITY OF LIVING CELLS. 



The work just described shows that salts enter living 

 cells, but throws no light upon the question of whether 

 penetration is effected by the ions or by the undissociated 

 molecules. To decide this question, Osterhout (1912, 1) 

 made conductivity measurements upon living cells in 

 various solutions. For this purpose material which is not 

 injured by weak currents must be employed. It should 

 also be uniform in texture. In addition it is desirable 

 that the current should pass through as large an area as 

 possible to miriimize the effect of local irregularities. This 

 is most readily secured by using thin sheets of tissue closely 

 packed together and separated only by films of the solu- 

 tion. The sheets should also be sufficiently rigid to permit 

 of manipulation involving the application of pressure to 

 insure that the solution films are very thin. 



Such conditions being all fulfilled by the fronds of 

 varieties of Laminaria, these were accordingly used by 

 Osterhout throughout the investigations. 



