155 



a. tlie number of calcium-ions placed or not placed over against 



iinivalent-ions. 

 h. the number of H-ions. 

 c. the amount of light incident upon the heart, especially in the 



presence of a fluorescent substance. 



1 VWWVW*— »/^ 



,^_^S— M^MvJv^KM 



LJLÜ 



Fig. 2. 



Eel's heart in situ. Perfusion from vena cava, first with a circulating fluid, 

 containing 15 mgr. thorium-nitrate per litre, then with a circulating fluid, containing 

 100 mgr potassium-nitrate. 1 sinus, 2 atrium, 3 ventricle. Time in sec. At S 

 transition from one fluid (thorium-beat) to the other (potassium-beat). Only in the 

 ventricle a light tonus is noticeable during the thorium-beat. It has disappeared 

 already for the greater part in the first beat performed by the heart during the 

 paradoxon. 



When applying uranium as an «-rayer each of the three above 

 conditions is modified. Sub a undergoes a change because over 

 against the calcium-ion not only univalent ions are placed, but 

 also uranyl. Sub h is modified, because a solution of uranyl-salt 

 causes a small increase of H-ions in Ringer's solution. True, this 

 factor may be eliminated by the addition of a trace of CaCO,, but 

 let it be supposed that this did not take place. Sub c has been 

 modified, because in the organ perfused with a potassium-fluid the 

 incident light has only an inappreciable influence uniessits strength 

 be enormous, while in the presence of a fluorescent uranium-liquid 

 also oidinary light will show its tonic action. 



It will, therefore, be considered quite rational that in fig. 1 the 

 bases of the uranium-elevations are not so low as those of the po- 

 tassium-elevations. When thorium is substituted for uranium the 

 phenomenon is less pronounced, still, it is certain that even then 

 the tonus is not quite absent. 



