Cellular Aspects of Body Electrolytes and Water 23 



are not in osmotic equilibrium with their extracellular fluid 

 has been seriously maintained, and an "osmotic pump", 

 driving water continuously out of the cell, has been postu- 

 lated. The experimental basis for this claim rests on the 

 observation that mammalian tissue slices, in particular 

 those of liver and kidney, swell when placed in "isotonic" 

 solutions of sodium chloride, Tyrode or Krebs (Sperry and 



♦ Figure in brackets for sodium represents, according to Conway, the true intracellular con- 

 centration. 



Brand, 1939; Opie, 1949), either at room temperature or at 

 0°. Robinson (1952) observed that the swelling could be 

 prevented or reversed by maintaining the tissue at 37°; he 

 found also that the swelling occurred in the presence of cyanide 

 at this temperature. Since swelling was prevented by using 

 strongly hypertonic solutions — 0-55-0 -60 m — he concluded 

 that the cells were iso-osmotic with these. It will be quite 

 clear from what has been said earlier that these facts may be 

 explained just as easily on the assumption that the electrolyte- 



