Physiology. — "On the behaviour of the Uranium-heart towards 

 Electric Stimulation, as investigated by Mr, M. den Boer. 

 By Prof. Dr. H. Zwaardemaker. 



(Communicated in the meeting of May 26, 1917). 



When an isolated Kroneckered frog's heart, after being freed from 

 circulation-potassium, is fed with a uranium-containing fluid (15 mgrms 

 of nranyl-nitrate '), 100 mgrms of calcium-chloride, 200 mgrms of 

 sodium-bicarbonate, 7 grms of sodium-chloride per Litre) it will soon 

 recover its automatical pulsations and also its mechanic excitability 

 in a most perfect way. If to such a heait we apply during the 

 diastole, electric stimuli in the form of opening induction shocks of 

 moderate force, the usual extrasystoles will be produced when the flow 

 of uranium begins. Later on when the uranium-circulation has continued, 

 say, 15 minutes, and when the uranium-salt has penetrated into all 

 lacunae and cell-walls, a short pause will still be observable after a 

 stimulus given at the right moment, but ultimately no manner of action 

 will be seen any more. When the uranium condition of the heart is 

 complete, the ventricle has become electrically inexcitable. Mechanical 

 excitability continues, though slightly diminished "). 



If the single induction shocks be replaced by a series of "making" 

 and "breaking" shocks, strong enough to produce extrasystoles, 

 something very striking takes place. We procured the said periodic 

 stimuli by causing the teeth of a rotating disc to be dipped into a 

 little mercury, the disc being so driven by a small electromotor 

 that the time of closure of a current (from an accumulator of 2 

 volts) is equal to the time of opening. In this way we effectuated 

 500 closures and 500 openings per minute, affording in all 1000 

 stimuli per minute. When they were sent in some direction or other 

 through the normally pulsating uranium-heart, a standstill in diastole 

 ensued in tyjucal cases almost without a latent period. On discon- 

 tinuing the stimulation the heart resumes its beats suddeidy with 

 normal rhythm and with perfectly regular systoles, perhaps after 

 a short after-effect. 



1) Winter-frogs require 25 mgrms, summer-frogs from 1 to 5; in this case we 

 took an average quantity. 



^) Gf. H. Zwaardemaker Potassium-ion and automaticity of the Heart. Ned. 

 Tijdschr. v. Geneesk. 1917, I, p. 1174. 



