441 



When instead of presenting a short stimulus, tlie current is sent 

 through permanently, at first a marked quickening of the riiythni 

 will be noted, attended with a marked positive inotropic efieci. 

 This is apparently iin accelerans etfect. 



Pig- "■^■ 



Petromyzon fluviatilis. 



Fatigue of accelerans and vagus through permanent stimulation from 



medulla oblongata. The stimulus starts at the lust elevations. 



C. d. 143. This continues as far as the stroke. Time 10 sec. 



When breaking the current during this period a standstill will 

 rapidly ensue, which will disappear again directly- aflei' fresh stimu- 

 lation. When, however, the current passes continuously, a slower 

 rhythm will appear after some time spontaneously viii tig. 2 ± 3(J 

 seconds), while at the same time the height of the contractions 

 diminishes gradually, it is the transition to a distinct vaguselfect. 

 When this rhythm has also continued for some time (in fig. 2 about 

 1 min.), it will change into a rhythm that is only slightly quicker 

 than the normal, or does not differ from it at all, and will persist 

 unaltered after the breaking of the current. 



When perfusing the animal with a potassium-free uranium-con,- 

 taiidng, instead of a potassium-containing fluid we shall see that ihe 

 phenomena are practically the same in the K-, and in the U-condilion. 

 First we see an acceleration, then a retardation, which in some 

 cases is followed again by an acceleration. This, however, is never 

 so pronounced as at the beginning of the stimulation. 



What has been said above goes to show that : 



1. in Petromyzon fluviatilis cardio-regulative nerves are present. 



2. with the technique employed after the removal of curari the 

 excitability of the cardiac nerves returns sooner than that of the 

 motor nerves. 



3. in the curarized animal the latent period of the accelerans is 

 shorter than that of the vagus. 



