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An increased KCl percentage caused an increased frequency until 
the contractions became too slight to be registered, whilst a decreased 
KCl pere. resulted in a decreased frequency, 
Hence under the action of KC] the sinus likewise behaves in a 
manner directly opposite to that effected by CaCl,; the differences 
in the diagrams are, however, more pronounced. No reasons have 
been found hitherto which may justify the conclusion that, also 
with regard to KCl, there is only a difference in degree between — 
auricle and ventricle. } 
Just as with CaCl, the contractility did not differ from that of 
the ventricle. It decreased at an increased KC] percentage and could 
hardly be registered already in diagram Il at 0.02°/, and in diagram 
[V at 0.03°/,. A decrease of the KCl percentage, however, caused 
it to increase. When a solution containing no KCI was led through 
the sinus, the contractions became indeed smaller after the process 
had lasted for hours, but they never disappeared, so that it cannot 
be determined from these experiments whether KCl is absolutely 
necessary for the sinus-automatism. 
Further the experiments gave an impression that the sinus as a 
rule responded more slowly to changes in the concentration of 
the KCl than of the CaCl,. To concentration changes of the 
NaCl it mostly responded more quickly than to changes in the 
CaCl, percentage. 
As regards the tonus it was discovered that, just as with the 
ventricles, it decreased when the KCl perc. was raised and increased 
when it was lowered. | 
Nall. 
The decrease of concentration caused by NaCl was investigated 
only while the osmotic pressure was kept constant by means of 
cane-sugar. 
Again the frequency was directly opposite to that of the isolated 
ventricle, as appears from the diagrams V, where 0.01°/, of CaCl, 
6 aq had been added, and VI where 0.01 °/, without aq. was used. 
See also fig, 4. When the amount of CaCl, was small, greater 
quantities of NaCl could be withdrawn than when it was greater. 
If the concentration was weaker than the minimum values marked 
_on the diagrams or even equal to 0, then the concentrations stopped 
within a few minutes, which makes a great difference with KCl 
and CaCl,. 
The contraction-height mostly increased a little at first; then it 
