Physiology. — ,,/s Caesium Radio-active?" By Prof. H. Zwaarde- 

 MAKER, W. E. Ringer and E. Smits. 



(Communicated at the meeting of June 30, 1923). 



Up to tlie pie.sen( potassium and riibidinm are (he only elements 

 in tiie series Li, Na, K, Rb, Ca, wliioli have been proved lo be 

 radio-active. It has often been suspected that caesium also possesses 

 a sMght radio-aclivitj, but thus far tliis is not certainly known. 

 E. Rutherford') simply remarks tiiat caesium is barely I'adio-aclive 

 and St. Meyer and E. von Schwindi.er') suggest that radio-activity 

 may possibly exist, but the penetrating power of the rays emitted 

 is so low thai it does not reach beyond the limits of the substance. 

 We know for certain that commercial preparations of caesium exert 

 no photographic action, even in exposures for months. Neither could 

 one of us') detect in carefully purified caesium preparations any 

 ionization of the air of a tlat ionization-chamber. 



It is a fact, however, that biologically caesium exerts in many 

 cases an influence similar to that of potassium and rubidium. This 

 influence was already known lo Sidney Ringkr *) and has, moreover, 

 been purposely studied by one of us.') After au unsuccessful effort 

 in winter we succeeded in the summer of 1917 in keeping hearts 

 of coldblooded animals beating on a dosis of caesium-chloride that 

 only slightly differed from the usual potassium-dose. It appeared that 

 potassium-, rubidium- and caesium-chloride could be used promis- 

 cuously, but thai a much larger quantity of caesium had to be 

 applied for a toxic effect. With regard to uranium, thorium, radium, 

 and radium-emanation it behaved antagonistically, which was after- 

 wards also confirmed by Miss L. Kaiser °). 



Here, then, a contrast manifested itself. Physically well-purified 

 caesium-compounds are to be considered as non-radio-active, whereas 



1) E. Rutherford in Marx's Hdb. der Radiol. Bd. II S. 531, 1918. 

 ^) St. Meyer und E. v. Schwindler, Radioaktivitat, 1916 S. 428. 

 ») W. E. Ringer, Arch, néerl. de Physiol, t. 7 p. 434, 1922. 

 *) S. Ringer, Journal of Physiol. Vol. 4 p. 370, 1883, 



5) H. Zwaardemaker en G. de Lind van Wijngaarden, K. Akad. v. Wetensch. 

 27 Oct. 1917, Proc. vol 20 p. 773. 



•) L. Kaiser. Arch, néerl. de Physiol, t. 3 p. 587, 1919. 



