54 ABSORPTION AND RETENTION OF POTASSIUM 



physiological behavior. This work is reported in another paper (1 4) , but 

 may be briefly summarized in so far as it applies to the subject under 

 discussion. It included experiments in which frog's legs were perfused 

 with a Ringer solution whose potassium chloride was replaced by 

 equivalent amounts of rubidium or cesium chloride. The muscles 

 of one leg were meanwhile stimulated to contract without complete 

 fatigue. Subsequently both legs were perfused with a potassium-free 

 Ringer solution until the outgoing fluid gave no spectroscopic test 

 for rubidium or cesium. The muscles of both legs were then analyzed 

 for rubidium or cesium. Only those of the leg which had been stimu- 

 lated during the first perfusion showed the presence of these metals. 

 To take them, and therefore their close homologue, potassium, into the 

 muscle in such manner as to be retained, in a non-diffusible form 

 would seem to require contractile activity of the muscle. 



DISCUSSION. 



These experiments indicate that, as Loeb (1) has suggested, the 

 potassium of muscle cells can be considered as existing in two different 

 states. The portion constituting one of them is comparatively mobile, 

 consists of about 15 per cent of the muscle potassium in summer 

 frogs and a smaller proportion in winter frogs, and can be removed 

 from frog muscle, under the conditions described, by mere perfusion 

 with a potassium-free Ringer solution. The rate of its loss seems to 

 be unaffected by contractile activity of the muscle. The remainder of 

 the potassium, amounting to approximately 15 per cent of the dry 

 solids of a perfused muscle, markedly resists outward diffusion but 

 is liberated and rapidly lost when the muscle is stimulated to an 

 extreme stage of fatigue. That some deep-seated change in the 

 chemical composition of a muscle occurs during unusually prolonged 

 exertion is evident from the long duration of the after effects. That 

 the change causes an alteration of the conditions governing the parti- 

 tion of inorganic constituents between dissociable and non-dissociable 

 forms is suggested by these observations. The greater osmotic 

 pressure of fatigued muscle as compared with non-fatigued was shown 

 by Moore (15) and taken to indicate an increased concentration of 

 electrolytes in the cell during contraction unless they are removed by 

 the circulation. The work of Loeb (16) showing the absolute 



