p. H. MITCHELL, J. W. WILSON, AND R. E. STANTON 145 



both legs showed good response to both direct and nerve stimuli; 

 though, to the same stimulus, muscles of the right leg responded, of 

 course, more vigorously than those of the left. Adequate samples 

 of muscles of the right legs (amounts of samples are recorded in the 

 table) showed no trace of cesium in a careful spectrum analysis. 

 Muscles of the left legs showed brilliant cesium spectra, permitting 

 a quantitative estimation. Cesium, then, like rubidium was taken 

 into the muscle substance so as to be retained, in part, during the 

 subsequent perfusion with potassium-free Ringer solution. 



To further test the replaceability of potassium by rubidium and 

 cesium young white rats were fed on purified synthetic diets in which 

 salts of rubidium or cesium were substituted for those of potassium as 

 ordinarily used in such diets. The basal diet had the composition 

 shown below. 



per cent per cent 



Casein 18 Dried yeast 5 



Starch 54 Salts 5 



Butter fat 18 



In the experiments with rubidium each 5 gm. of salt mixture con- 

 tained approximately: 



gm. im. 



MgS04 • 7H2O 0.55 CaH4 (P04)2 • H^O 0.54 



NaHaPO^ • 4H2O 1 . 10 Calcium lactate 1 .40 



RbCl 1 .29 Iron lactate 0. 12 



In the cesium experiments each 5 gm. of the salt mixture con- 

 tained approximately: 



gm. {M. 



MgS04 • 7H2O 0.46 CaH4 (PO^)^ • H2O 0.45 



NaH2P04 • 4H2O 1 .27 Calcium lactate 1. 12 



CsCl 1 .59 Iron lactate 0.11 



Water was given freely and to it a few drops of iodine solution 

 were added once a week. The animals were put in separate 

 cages, weighed frequently and kept under observation. After 

 varying periods (10 to 15 days) the rats showed marked symp- 

 toms of derangement. We noted a sluggishness and general 

 inactivity, followed by a period of marked irritabihty, with trem- 

 bling and intermittent twitching which later amounted to tetanic 

 spasms. Within 48 hours after the first tremblings were noted 



