310 PROTOPLASMIC ACTION AND NERVOUS ACTION 



Such facts suggest that substances having the proper- 

 ties of weak acids determine the type of electromotor 

 behavior shown by the cell surfaces in the demarcation 

 potentials. Both proteins and lipoids (e.g., lecithin) belong 

 in this class. Loeb and Beutner^ therefore carried out 

 further experiments of the kind described, using solutions 

 of lecithin in organic solvents, and found again the same 

 relation between the concentration of the salt and the 

 observed potential difference. When lo per cent solu- 

 tions of lecithin in guaiacol were used, the behavior, both 

 quahtative and quantitative, was found closely similar 

 to that of plant tissues. Oleic and palmitic acids gave 

 similar results, but not cholesterol. Extracts of various 

 plant and animal tissues (muscle, brain, frogskin) in 

 organic solvents also exhibited this behavior; a further 

 interesting fact was that potassium salts had a greater 

 influence than sodium salts in altering the potentials, 

 a pecuHarity which the authors ascribe to a greater 

 solubiHty of potassium salts in the lipoid phase. 



It would seem, therefore, as if the ordinary potential 

 differences observed between altered and intact portions 

 of the cell surface were phenomena of the same general 

 type as those just described; i.e., referable to the 

 presence of a water-insoluble phase containing weakly 

 acid substances and forming a thin film or partition 

 between two dissimilar electrolyte solutions, represented 

 respectively by the living protoplasm and its surrounding 

 medium.^ 



^ Biochem. Zeitschrift, LI (1913), 288. 



' As to the specific nature of the electrolytes concerned, little definite 

 can be said at present. In general the two cations whose concentration is 

 higher inside than outside the cell are K and H. A recent calculation 



