1047 
In contradistinction to the remarkable analogy between potassium 
and uranium (present in the fluids respectively as potassium-ion and 
uranyl-ion) there is a no less remarkable antagonism. When a heart, 
that beats well when fed with a potassium-containing fluid, is supplied 
with a circulating fluid containing per litre 25 mgrms of uranyl- 
nitrate instead of 100 mgrms of potassium-chloride, it stops suddenly. 
And conversely when a potassium-containing fluid is given to a heart 
which beats normally with a uranium-containing fluid, it is also 
brought to a standstill. Not before many minutes later do the auto- 
matic contractions recommence. The very same takes place when 
the normal potassium-containing fluid is administered after a fluid 
containing thorium or radium or emanation. Not, however, when 
the heart is supplied with first rubidium and then potassium or vice versa. 
Nor when a_uranium-containing flnid succeeds one containing 
emanation or the reverse. It is evident, therefore, that, when applied 
in succession the lighter elements compensate each other, just as 
the heavier ones do. On the other hand the two groups are mutually 
antagonistic. When applied successively, they arrest the cardiac action; 
when applied singly, each sustains it for an indefinite space of time. 
A mixture of potassium and an equal amount of rubidium causes 
the heart to beat; the same holds for an equal apportionment of 
uranium and thorium; but potassium combined with uranium or 
thorium, or a combination of rubidium and uranium stop the heart’s 
pulsations. Thus the lighter and the heavier elements are reciprocally 
antagonistic not only when acting successively, but also simultane- 
ously. The following graph shows the ratios of the potassium-uranium 
antagonism when acting simultaneously. 
Uranium Potassium-Uranium antagonism 
mgr. p. L. 
200 mgr. CaClo ks 
…__e 900 mgr. CaCl, p. L. 
Oee TT 
4 Potassium 
mgr. p. L. 
0 20 40 60 80 300 380 40 300 180 Wo 20 
Fig. 3. 
The points indicate the combinations with which the heart was 
reduced to astandstill. In the mixtures lying above the continuous line 
the cardiac action was restored by the influence of an excess of 
potassium; in the mixtures below the continuous line pulsation recom- 
