LIBRARY 



NK\y vi^jc 



CONDUCTIVITY AND PERMEABILITY. 



By W. J. V. OSTERHOUT. 



{Fram the Laboratory of Plant Physiology, Harvard University, Cambridge.) 



(Received for publication, July 19, 1921.) 



When an electrical current passes from a salt solution into a living 

 cell, ions must enter the protoplasm. An increase in the permeability 

 of the protoplasm to ions must decrease its electrical resistance, and 

 vice versa. The electrical resistance of the protoplasm may there- 

 fore be regarded as a measure of its permeability to ions. 



If we attempt to measure the electrical resistance of the protoplasm 

 we must first consider the structure of the tissue. For example, we 

 find in the case of Latninaria that the protoplasm of each cell forms 

 a thin layer which surrounds a large central vacuole filled with cell 

 sap. Since experiments have shown that the cell sap has about the 

 same electrical resistance as the solution which bathes the cell, it 

 is evident that when the electrical resistance of the cell increases, 

 on transferring it from sea water to another solution of the same con- 

 ductivity, the change must be due to an increase in the resist- 

 ance of the thin layer of protoplasm which bounds the cell. This 

 has led the writer to assume that the resistance is proportional to a 

 substance, M, at the surface of the cell; if M forms a layer at the sur- 

 face it is obvious that an increase in the thickness of this layer will 

 increase the resistance, and vice versa. It is therefore assumed that 

 the resistance depends upon the amount of M which is present in 

 the surface.^ 



In Latninaria the protoplasmic masses (cells) are separated from 

 each other by a thin layer of gelatinous substance (cell wall). In 

 passing through the tissue a part of the current goes through the 

 protoplasm and another part passes between the protoplasmic masses^ 



_ ' This assumption is simple and facilitates quantitative treatment. It is recog- 

 ^ nized that changes in resistance might depend upon other properties of this layer, 

 ^ — and that the layer need not necessarily be continuous. 

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