INJURY AND RECOVERY 87 



then placed in NaCl 0.52 M, which had the same conduc- 

 tivity as the sea water ; at the end of 10 minutes the resist- 

 ance was 85.4%. The experiment was continued by 

 placing the material for 10 minutes alternately in CaCl 2 

 and NaCl, with the results shown in Fig. 36. After 80 

 minutes the material was placed in sea water, where it 

 soon regained its normal resistance: 24 hours later the 

 resistance was found to be unaltered, and the experiment 

 was repeated. After 80 minutes of alternate exposure 

 to CaCl 2 and NaCl, the material was placed in sea 

 water, where it soon regained its normal resistance, 

 which it maintained for 3 days, when the experiment 

 was discontinued. 



Similar results 11 were obtained with Ulva (sea let- 

 tuce), Rhodymenia (dulse) and Zostera (eel grass). 

 Recovery was also observed with frog skin. 12 



The fact that protoplasm is able to endure such vio- 

 lent alterations of conductivity throws a new light on the 

 normal life processes of the cell. In the course of met- 

 abolism a great variety of substances are produced which 

 affect the permeability of the protoplasm. Since it is 

 clear that the permeability may be greatly increased or 

 decreased without rendering a return to normal permea- 

 bility impossible, it is evident that considerable fluctua- 

 tions in permeability may form a normal part of the 

 life processes of the protoplasm. In this way the whole 

 course of metabolism may be controlled, since this depends 

 on the exchange of substances between the cell and 

 its environment. 



It is a striking fact that normal specimens of 

 Laminaria are quite uniform in respect to electrical resist- 



"C/. Osterhout (1919, A). 

 12 Cf. Osterhout (1919, C). 



