144 



ABSORPTION OF RUBIDIUM AND CESIUM 



sodium content of the solutions of wet-ashed muscle. The samples 

 taken from the stimulated muscles were 1.86 gm. from the gastro- 

 cnemius, and 2.03 gm. from the vastus. The standard solution diluted 

 3.5 times gave the faintest rubidium spectrum possible to detect. The 

 solution from the gastrocnemius behaved similarly when diluted 3 

 times and the one from the vastus when diluted 3.5 times. A careful 

 uniformity of technique was used in making all the flame tests. This 

 estimation shows 0.011 per cent of rubidium in the gastrocnemius 

 and 0.012 per cent in the vastus. As a matter of fact a proportion 

 of rubidium larger than these figures indicate was present because 

 the muscles were obviously edematous. Rubidium content, in pro- 

 portion to the dry solids, was not estimated. An amount of rubidium, 

 equivalent to more than 3 per cent of the normal potassium content 



TABLE I. 

 The Absorption and Retention of Cesium by Frog Muscle 



of frog muscle, was taken up when the muscles made 540 contractions 

 of 1 second each. The retention of rubidium in the muscles during 

 perfusion vidth a rubidium-free solution and the absence of rubidium 

 from the unstimulated muscles, points to its actual entrance into and 

 incorporation vdth the cell substance in the same sense that potassium 

 is normally held there. Whether or not it actually replaces potassium 

 has not yet been determined. 



Similar experiments were made with cesium chloride, replacing, in 

 equimolar concentration, the potassium chloride of Ringer solution. 

 The data of two such experiments are presented in Table I. The 

 muscles of the left leg of the frog used in each experiment made 420 

 contractions of 1 second each, Vv^hile the cesium-containing solution 

 was perfusing through both legs. The muscles of the right leg were 

 meanwhile at rest. At the end of the experiment the muscles of 



