154 



similar need for radio-activitj in the several subdivisions of the 

 heart. This is seen best when passing from a perfect uranium-dosis 



Fig. 1. 



Frog's heart Kronecker's canula 14° C, red light. 



Transition from a circulating fluid with 25 mgr. uranylnitrate to another with 

 300 mgr. potassiumchlorid per litre, and then back again to 25 mgr. uranylnitrate. 

 The transitions generally took place resp. 40 and 60 seconds before the paradox- 

 ical standstills, indicated in the figure by a white line. Potassium pulsation in the 

 centre. Time Ye "^i^i- 



to a perfect potassium-dosis or the reverse with a simultaneous 

 registration of the sinus, atrium, ventricle. If no conductive disturb- 

 ances occur, it will be seen that the three divisions of the heart 

 will stand still and resume their beats at the same moment with 

 automaticities of their own. This is illustrated below in fig. 2 for 

 an eel-heart in situ, which was perfused first with a uranium-liquid 

 and at a moment designated in the time-line by /5 with a potassium- 

 liquid. 



The phenomenon, instanced in fig. 2 requires, however, accurate 

 dosage of uranium as well as of potassium. It would not be surprising, 

 if inaccuracj' in this respect should engender dromotropism. 



A third property the two automaticities have in common is 

 the self-regulation after extrasystole, for «-conditions as complete as 

 for the /i-conditions. 



The fourth common property is the initial similarity of the alpha- 

 and the beta-electrogram, though I must admit that afterwards a 

 difference may come forth through secondary influences ^). 



Only in adventitious respects do the two automaticities differ. 



Of the greatest importance in this respect is the tonicity of the 

 heart. The conditions determining the auto-tonus of the cardiac 

 muscle are: 



1) Klinische Wochenschrift Jahrg. I W. 12 (or Diss. H. Sloofp, Utrecht 

 4 July 1922). 



