654 
April 28 and May 27, 19165, in which the elements K., Rb., U., 
and Th. have been mutually compared. Their doses in the physiolo- 
gical solutions, used by Feenstra are in the ratios of their total?) 
radio-activities. The experiments were performed chiefly upon the 
frog’s heart. It kept beating for hours in every one of the solutions, 
just as with the best prepared RINGER’s mixture, in common use. 
From the very beginning we have, moreover, proposed detecting 
at the same time any antagonism for the salts, in which the radio- 
active elements are used. Antagonism was found indeed and appeared 
to be primary, i.e. it concerns the system in which the excitability 
of the heart muscle arises automatically and spreads, for the 
antagonism affects the electrocardiogram as well as the myogram. 
Besides all reactions are reversible. 
Finally the element Radium bas also been examined in the same 
way. 
The apparatus were arranged as before. A frog’s heart, removed 
from the body, was first fed for fifteen minutes by means of a 
KRONECKER cannula with normal Rrincer’s mixture (NaCl 0.7 °/,, 
KC10.01; CaCl, 0.02; NaHCO, 0.02, glucose 0.1), to enable it to 
restore itself. Subsequently Potassium-free Rincer’s mixture was 
given until, after a short retardation and irregularity, a standstill 
ensued. Only in the third place followed the administration of a 
potassium-free RINGER’s mixture to which radium-bromide had been 
added to an amount, which, as far as its total radioactivity is 
concerned, may be considered about equal to the amounts of K., 
Rb., U., and Th., used in previous experiments. 
The radium at the disposal of Mr. Feenstra was obtained of the 
Radiogen-Gesellschaft, branch-office at Amsterdam and was equal to 
1000 Mache-units per litre of the original fluid. In the 7 ce. mixed 
with one litre of potassium-free Rincer’s mixture this corresponded 
with about 3 micromilligrams (3.109 gram). 
The small quantity of the solution supplied by the Company, 
which was to be one of the constituents of the circulating fluid, 
was neutralised beforehand and the fluid was used immediately 
afterwards in order to prevent a slow precipitation of the radium- 
salt in unacidulated fluids *). 
Thus we invariably succeeded in 10 + 3 experiments in making 
1) T. P. FEENsTRA, See these Proceedings Vol. 24 p. 1822; Vol. 25 p. 37 1916. 
2) Total radio-activity after RuTHERFoRD’s data in Marx’s Hdb. d. Radiology, 
Vol. 2 p. 519, 525; the measurement for Potassium and Rubidium was performed 
according to data found here and there in the book. 
5) A. S. Eve, Amer. J. of Science (4) Vol. 22, 1906 p. 4. 
