101 
This solution, which contains all the substances (except potas- 
sium chloride) of which Locku-Rinerr’s solution is composed, might 
be called a “potassium-free Rineer’s mixture”. We will, for con- 
venience’ sake, denote it in this paper by the symbol R.-K. 
From this solution we first made Rinexr’s mixture by adding 100 
mgrms of potassium chloride per litre. If we allowed R.-K. to run 
through a frog’s heart, it was brought to a standstill in diastole 
after an interval different for each heart. The shortest interval noted 
was in the neighbourhood of 10 minutes, whereas another heart 
stopped beating only after five quarters of an hour; with the remaining 
hearts the times varied between these two extremes. If we subse- 
quently sent the same solution with an addition of 100 germs. of 
potassium through the heart its normal pulsation was restored spon- 
taneously. Obviously the absence of potassium had brought about 
the arrest of the heart. 
Of the new group we first examined the uraniumcompounds. 
After tying up the heart and allowing Rineer’s mixture to pass 
through it for about 15 minutes, in order to completely restore its 
normal beats, it was brought to a standstill with R.-K. Then a 
stream of R.-K. to which 25 mgrms of uranium-nitrate (U(NO,),) 
per litre had been added was circulated through the heart, which 
resumed its beats regularly and spontaneously after an average in- 
terval of about five minutes, just as at the beginning of the expe- 
riment when RINGER’s mixture was administered. 
This phenomenon I observed in 16 different experiments; to my 
knowledge there was no case in which the uranium containing R.-K. 
remained inoperative. What I did observe was, that, if the heart 
was fed with the ordinary RiNGer's mixture subsequently to the admi- 
nistration of uranium-containing R.-K., the heart immediately stopped 
beating in diastole, and could be made to resume its normal fune- 
tion only either by R.-K. or by uranium-containing R.-K. The stand- 
still which in this case was induced by the application of RinegEr’s 
mixture, occurred almost directly after the beginning of the inflow. 
If the heart began to pulsate again after its arrest, this occurred 
abruptly, the contraction and the electrocardiogram regaining at once 
their normal extent and frequency, while the tonicity was not modi- 
fied in the process. Here, therefore, it was a case of ‘“all-or-none”’. 
The contractions also persisted as at the beginning of the experiment. 
If, however, the circulation of R.-K. had not removed a sufficient 
amount of potassium chloride from the heart at the beginning of the 
experiment, in consequence of the standstill being incomplete at this 
juncture, the cardiac action was not restored, neither with uranium- 
