200 INJURY, RECOVERY, AND DEATH 



Since the protoplasmic masses (cells) are separated 

 from each other by thin layers of substance (cell wall) a 

 part of the current gbes through the protoplasm and 

 another part passes between the protoplasmic masses, 

 in the substance of the cell wall.* Consequently when we 

 employ the electrical method we must ascertain 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 cannot 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 therefore evident that the changes are 

 due to the living protoplasm. 



The cell wall appears in all cases to have practically 

 the same conductivity as the surrounding solution. If 

 we subject living tissue to solutions of the same conduc- 

 tivity, but of different chemical composition, the resist- 

 ance 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 CaClj (of 

 the same conductivity as sea water) its behavior differs. 

 In NaCl the resistance falls ; in CaCl2, it rapidly rises and 

 later falls to a minimum. We infer that the permeability 



'As previously explained (Cf. Osterhout, 1918, G), a part of the 

 current must pass through the protoplasm; this is shown by the fact that 

 CaCla (which has little effect on the resistance of the cell wall) raises the 

 resistance of the tissue and that the temperature coefficient of electrical 

 conductivity is not the same for dead as for living tissue. 



