464 > 
frequency -— before the ultimate quantity has been diffused. It was 
found that in nearly all the experiments the number of contractions had 
indeed decreased somewhat after 5’, and had reached its original 
value again after 10’ or 15’. (See table p. 463). 
In weak concentrations the effect of both substances on the excursion 
was a favourable one; in greater concentrations it was now favourable, 
now unfavourable. 
The effect on the tonus was so little pronounced that we must 
abstain from expressing an opinion on the subject. 
Summary. 
From these experiments it appears that there is indeed « great 
difference between the sinus and the isolated ventricle of the frog; 
they behave in directly opposite ways, as regards frequency under the 
influence of Call, KCT and NaCl. 
When the physiological dose is increased KCI heightens and CaCl, 
lowers the frequency. 
When the physiological dose is diminished CaCl, slightly raises 
the frequency, and KCI and NaCl retard it. 
The fact that a copious withdrawal of CaCl, mostly lowers the 
frequency led to the supposition that the different behaviour of sinus 
and ventricle towards this salt, is merely a difference in degree. 
These facts were not observed in the case of KC] and NaCl. 
Tonus and deflection are like those of the ventricle. A slight 
increase of the CaCl, pere. of RiNcer’s fluid has a positive inotropic 
effect; with great quantities the effect is negative inotropic. The tonus 
is always raised. 
An increase of the KCl percentage has a negative inotropic effect 
and lowers the tonus. 
A decrease of the CaCl, percentage likewise lowers the tonus and 
results in a negative inotropic effect. 
A decrease of the KCl percentage has a positive inotropic effect 
and increases the tonus. 
A slight decrease of the NaCl percentage results perhaps in a 
positive inotropic, a great decrease in a negative one. Probably the 
tonus is heightened. 
An increase of osmotic pressure by means of cane-sugar gives 
negative inotropic results, a quantity of urea with the same osmotic 
pressure leaves the frequency the same. It is highly probable that 
the muscular celis of the sinus are permeable to urea. 
Further it appeared from these experiments that of frequency, 
tonus and deflection the former is by far the most constant. 
