1162 
circulating fluid, are neutralised by uranium, thorium, radium, or 
emanation. To this series the radiation may be added, on the side 
of potassium and rubidium. Its effect may be neutralised when 
uranium or thorium are contained in the circulating fluid. 
This led me to investigate the quantitative relations coming to 
the front when placing a mesothorium preparation of 5 mgrms in 
a glass bulb at various distances and when to a neutral mixture 
of 40 merms of potassium chloride and 10 mgrms of uranylnitrate 
the quantum of uranyl-salt, required for each distance, was added. *) 
Let us consider a frog’s heart through which after the method of 
Kronecker has been sent first Rincer’s mixture and subsequently, 
for some time, a potassium-free circulating fluid composed of 7 grms 
sodium chloride, 200 mgrms of calcium chloride and 200 mgrms of 
sodium bicarbonate per litre. At a certain moment this inactive 
circulating fluid is replaced by one similarly composed to which 
has been added 40 mgrms of potassium-chloride and 10 mgrms of 
uranylnitrate. The heart thus supplied will soon lose its contractility. 
Next the preparation of 5 mgrms of mesothorium (in a glass bulb) 
is placed at a distance of precisely 8. 7, 6, 5, 4, 3, 2, 1 mm and we wait 
for the recommencement of the heart's beats, which on the average 
will take place after 13 minutes (minimum J, maximum 60 minutes). 
Now some uranyl nitrate in excess is added to the circulating 
fluid in a solution containing 1 mgrm of uranium salt per c.c. 
This procedure is continued for some time along with the radiation 
until the heart stops again. In this ease a slight touch will 
engender one systole. Should there be a short series at first then 
the wanted equilibrium is not yet obtained and a little more 
uranium has to be added. At length a standstill will ensue and 
may be maintained for 5—10 minutes (we took 5 minutes with a 
comparatively quick flow and 10 minutes with a tardy one). 
The looked for equilibrium between radiation on the one hand 
and uranium in excess in the circulating fluid on the other was 
found at the following distance (See table p. 1163) 
The equilibruim once established the relations may be altered 
again. The mesothorium may be moved nearer to the heart, or a 
larger quantum of uranium salt may be added. Hither process is 
responded to by the heart’s contraction and a second equilibrium 
may be looked for. In this way we often succeeded in finding even 
three successive equilibria. 
8 
1) 1 have to thank Mr. T, P. Feenstra assistant in the Phys. Lab. for his 
painstaking assistance in these experiments. 
