440 



primary circuit. The Pfeilsignal, which was used sometimes (e.g. in 

 the first figure), could not be placed in shunt, so it came in the 

 primary circuit. The obtained coil-distances (C. d.) are smaller than 

 when no signal is connected up. On stimulation we note a considerable 

 acceleration shortly after the stimulus has been set u[). If the 

 stimulus continues a short time only (in fig. 1 5 seconds) the 

 acceleration will be seen to disappear soon and to be substituted 

 by a retardation ; in case the latter increases, the heart is brought 

 to a standstill. After cessation of the negative chronotiopic effect, 



Fig. 1. 



Accelerans-vagus effect. 



Petromyzon fluvialilis. Perfused with Ringeh's mixture. Stimulation 



for 5 seconds of medulla oblongata of the level of tiie exil of the 



N. vagus. G. d. 100. 



The tracings from above downward : record of atrium movement 



, , stimulus signal 

 , , time line 10 sec. 



a new rhythm appears, more rapid than the original. A little later 

 it gives way to the old rhythm. In fig. 1 the rhythm prior to the 

 stimulation is ± 45 beats per minute, after the standstill the 

 frequency amounts to 55. The action of side-currents upon the 

 heartmuscle need not be taken into consideration in these experi- 

 ments, because the effect appears only wlieir a sharply defined area 

 in the medulla oblongata is stimulated and the effect is destroyed 

 again by a slight displacement of the electrodes. Besides this a great 

 influence is exerted by summation. A stimulus, for instance, that 

 produces no effect after 5 seconds, causes a distinct standstill after 

 a longer period. 



