Physiology. — ''On CaesuLin-ions and Cardiac Action'. By Prof. 

 H. Zwaardemaker. 



(Communicated in the meeting of October 27, 1917). 



Years ago Sidney Ringer'), in his study of the composition of 

 artificial circulating fluids, establislied that the isolated frog's heart 

 can sustain its beats for some time, if to an isosmotic, faintly alkaline 

 sodium-chloride solution, containing the necessary quantum of calcium, 

 caesium chloride is added instead of potassium chloride. Caesium salt 

 was substituted for potassium salt in an equivalent molecular amount. 

 When we carried out the same experiment last winter we did not 

 attain a definite result, but when we discovered this year that the 

 heart of the summer frog responds to smaller doses of potassium 

 chloride than the heart of winter frogs, we have undertaken again 

 Sidney Ringer's caesium experiment'). After augmenting the usual 

 calcium amount (200 mgr. CaCl^ per Liter) to 250 mgr. dry calcium 

 chloride (without w^ater of crystallization) the summer hearts could 

 be made to continue beating for an indefinite space of time by the 

 aid of an appropriate quantity of caesium chloride. Broadly speaking, 

 we can say that, for one heart, the dosis of caesium corresponds 

 with that of potassium and rubidium. The minimum dosis, needed 

 by a Kroneckered frog's heart in its Ringer's mixture, is smallest 

 in weight for potassium chloride, then follows most probably rubidium, 

 while the dosis of caesium chloride must be slightly larger. 

 Molecularly, therefore, the dosages may be called fairly equal. The 

 toxic dosis is a multiple; but we also found that, whilst (in summer) 

 double the dosis of potassium is in most cases toxic, the caesium- 

 dosis may be many times the minimum dosis that keeps the heart 

 beating. A little beyond the minimum dosis lies the optimum quantity. 

 In the months of September and October it amounted to about 

 40 mgr. CgCl per Liter of potassium-free Ringer's mixture. 



1) Sydney Ringer, Journal of Physiology. Vol. 4, p. 370. 



2) I was particularly prompted to do so, as the question was put to me by 

 Dr. C. E. BiicHNER, of Amsterdam whether it would be possible to demonstrate 

 biologically the radio-activity of caesium, which had often been surmised on account 

 of the relationship between this metal and potassium and rubidium. 



