2 CONDUCTIVITY AND PERMEABILITY 



in the substance of the cell wall.- Consequently when we employ 

 the electrical method we must fiscertain whether we are investigating 

 the permeability of the protoplasm or merely that of the cell wall. 



Obviously the best method of attacking this problem is to kill the 

 tissue by such means {e.g., partial drying, heating to 35°C., weak 

 alcohol, etc.) as can not alter the cell wall, and then investigate its 

 behavior under the influence of various reagents. We find that all 

 of these methods produce the same result. After death the tissue no 

 longer shows the changes in resistance which are observed when 

 living tissue is subjected to the influence of reagents. It is there- 

 fore evident that the changes are due to the living protoplasm. 



The cell wall appears in all cases to have practically the same con- 

 ductivity as the surrounding solution. If we subject living tissue to 

 solutions of the same conductivity, but of different chemical com- 

 position, the resistance of the cell wall remains unaltered while that 

 of the protoplasm undergoes great variations. If, for example, 

 living tissue is placed in a solution of NaCl or CaCla (of the same 

 conductivity as sea water) its behavior differs. In NaCl the resist- 

 ance falls; in CaCl2 it rapidly rises and later falls to a minimum. We 

 infer that the permeability of the protoplasm increases in NaCl; 

 and that in CaCU there is a decrease followed by an increase. 



This is in complete agreement with results obtained when permea- 

 bility is measured by such methods as plasmolysis,^ specific gravity,* 

 tissue tension, exosmosis, and diffusion through living tissue.* This 

 agreement indicates that the electrical method measures the permea- 

 bility of the protoplasm. It is however desirable to go further, if 

 possible, and analyze the factors involved in electrical resistance. 



^ As explained in a former paper (Osterhout, W. J. V., /. Biol. Chem., 1918, 

 xxxvi, 485) the fact that a part of the current passes through the protoplasna 

 is shown by the fact that CaCh raises the resistance of Hving tissue and by the 

 fact that the temperature coefficient of electrical conductivity dififers in living 

 and dead tissue. 



3 Osterhout, W. J. V., Science, N. S., 1911, xxxiv, 187. 



^ Loeb, J., Science, N. S., 1912, xxxvi, 637. Biochem. Z., 1912, xvii, 127. 



* Brooks, S. C, Proc. Nat. Acad. Sc, 1916, ii, 569. For exosmosis of the pig- 

 ment of RJiodymenia in relation to electrical resistance see Osterhout, W. J. V., 

 /. Gen. Physiol, 1919, i, 299. 



