774 



When this had been established^) for a good many cases, I went 

 into the question whether potassium-, rubidium-, caesium-chloride 

 could be used promiscuously, which I found to be the case. The 

 different substances may be alternated without any interval, provided 

 the dosis be well chosen. It is quite unnecessary, therefore, to inter- 

 polate a perfusion of a solution of merely 7 ^rms of NaCl, 200 mgrs 

 of NaHCO,, 250 mgrs of CaCl^ per Liter of pure water. If, however, 

 we administer, instead of a caesium-containing fluid, a fluid containing 

 uranium or thorium, we cannot maintain the cardiac action without 

 an interpolation. If there is still some caesium left in the heart, it 

 will come to a standstill when a uranium-, or thorium-fluid is sent 

 through, which in other cases would answer the purpose, as illustrated 

 by the subjoined flgures. 



A frog's heart, fed with a caesium- 

 fluid (40 mgr. of CaCl per liter of 

 potassium-free Ringer's mixture) and 

 beating vigorously, is rapidly per- 

 fused with a fresh thorium-solution 

 (20 mgrms of TIkNO')" per liter of 

 potassium-free Ringer's mixture) the 

 ^'S' ^' moment the curve in the flgure 



commences. The heart will stop in complete relaxation after three 

 minutes. After 25 minutes it will as suddenly recover its tonus and 

 commence a series of rhythmical beats. This behaviour is easily 

 accounted for. After the caesium-beats follows the caesium-thorium- 

 equipoise, which causes a standstill, whilst in the end the thorium 

 evokes new contractions. 



It will be remembered") no doubt that exactly the same phenom- 

 enon presented itself in a previous experiment in which potassium 

 or rubidium was replaced by uranium or thorium. There also 

 potassium- and rubidium-salts could be used promiscuously, nay 

 could even be mixed. The same holds good for uranium- and thorium- 

 salts. However, a potassium-, or rubidium-salt appeared to be anta- 

 gonistic to uranium or thorium-salt. The favourable eff'ect exerted 

 by every one of these salts per se is neutralized by the coincident 

 presence of a salt of the other group. The two actions counterbalance 

 each other, so that it is as if they do not exist and as if the heart 

 is in the same condition as it would be when left to itself without 



') Here I have much pleasure in thanking the assistant de Lind van Wijngaarden 

 for his painstaking help. 



») H. Zwaardemaker, Proceedings of 24 Febr. 1917, Vol. 25, p. 1096. (Proc. 

 Vol. 19, p. 1048). 



