46 ABSORPTION AND RETENTION OF POTASSIUM 



for the passage of potassium through the egg membrane and that 

 sufficiently prolonged action of pure water makes this membrane very 

 impermeable to potassium. But, as Loeb points out, the behavior 

 of the hatched embryo is very different from that of the egg. 

 In the egg we are dealing merely with the passage of potassium through 

 a comparatively distinct membrane but in the case of most cells we 

 must consider the taking up of potassium, whatever that means 

 physicochemically, by the cell acting as a whole. Salts are always 

 present and acidity absent in the medium bathing the great majority 

 of living cells. Hamburger (4) has shown that blood corpuscles, 

 washed with glucose solution, yield potassium to a potassium-free 

 Ringer solution, and Jannink (5) has reported that potassium is given 

 off by heart muscle during perfusion with a potassium-free solution. 

 Howell and Duke (6) recorded a liberation of potassium from the 

 heart perfused with Ringer solution during prolonged stimulation 

 of the vagus. These and other experiments, though they point 

 out interesting possibilities, do not reach the explanation of the 

 conditions limiting the entrance or exit of potassium, considering 

 cells in general. 



Muscle seemed a favorable material to use because it gives an 

 easily controlled range of physiological activity. The work of Lillie 

 and of McClendon indicates that, under some circumstances at 

 least, contracted muscles are more permeable than resting ones. 

 Is this true for potassium? We sought the answer to the question 

 by making determinations of the amount of potassium in frog 

 muscles after perfusion with various solutions either with or without 

 simultaneous excitation. The results have shown the great tenacity 

 with which the cells hold potassium while bathed in a potassium-free 

 Ringer solution irrespective of whether or not the muscles are made 

 to contract. As soon, however, as the muscles are fatigued beyond 

 physiological limits potassium diffuses out of the cells and as much 

 as half of their store may be lost in about 5 hours. Since potassium 

 is known to diffuse slowly from dead muscle and since extreme fatigue 

 in excised muscle is an irreversible process this was to be expected. 

 A study of the intermediate stage between mild activity and exhaus- 

 tion, showed that a part, from 8 to 15 per cent, of the potassium may 

 6e removed by perfusion, either with or without stimulation, without 



