2IO ELECTROLYTES IN BIOLOGICAL SYSTEMS 



These studies clearly show two facts: /) that in dead skin, inward osmosis 

 proceeds faster than outward osmosis; 2) that the metabolic processes in skin, 

 which means maintenance of respiration in our case, changes the skin in such 

 a way that outward osmosis now proceeds faster than inward osmosis. I have 

 no satisfactory explanation for either one of these observations. Referring to 

 'one-way osmosis' in the living skin, however, one may consider two possible 

 explanations. Either there is an active transport of water in the outward direc- 

 tion, simultaneous with active uptake of salt in the inward direction (23), or 



Fig. 4. Changes in the electrical properties of isolated frog skin {Rana pipiens) with 

 dilution of the outside solution. Relative concentrations with Ringer's fluid as unity. In 

 circuit B and C the cut edge of the skin served as reference point in the P.D. measurements 



(67)- 



the inwardly moving ions are partly stripped off of a loose shell of water. In any 

 event, the amount of water drawn through the skin by osmotic forces in the 

 outward and inward directions would be increased and decreased, respectively, 

 by the amount of water actively transported or released from ions. Another 

 factor involved may be this: if the inwardly moving ions were losing part of 

 their water shell, it could be visualized that this occurs at the walls of the pores 

 in the skin. As a result of this, one might think of a water film slowly moving 

 in the outward direction along the walls of the pores. If, then, an osmotic water 

 flow were forced upon this system, it would appear that inward flow would 

 meet with a greater resistance because of the outwardly moving water film. 



