ix CAEDIAC MUSCLE AND NEEVES 329, 



The inhibitory fibres arise in, the accessory or eleventh cranial 

 nerve. After extirpation of this nerve in the dog, and lapse 

 of sufficient time for the peripheral fibres running with the 

 vagus to degenerate, vagus stimulation produces no effect upon the 

 heart, as was shown by Waller in 1856, and subsequently con- 

 firmed by Schiff, Heidenhain, and Fran^ois-Franck. Giaunuzzi, 

 however, found that vagus excitation still produced a slight 

 moderator effect fourteen days after extirpation of the accessory 

 nerve, which he ascribed to certain fibres belonging to the vagus 

 itself, with the same function as those of the accessory. 



The accelerator fibres unite the lower cervical with the first 

 thoracic (or stellate) ganglion. They, too, emerge from the cord 

 (according to Strieker, in the first six thoracic nerves), and pass by 

 the rami communicantes to the sympathetic system. Albertoni 

 and Bufalini found the third dorsal nerve particularly effective 



Fir,. 151. Acceleration of heart-beats by brief excitation at E of the two branches of the nerve 

 that form the annulns of Vieussens, in cnrarised dog. (I)oyon.) Carotid connected with 

 Ludwig's kymograph. 



(Fig. 151). The cervical trunk of the vagus also seems to con- 

 tain some accelerator fibres, as shown by the action of atropin 

 (Eutherford). 



The functional character of the accelerator fibres was studied 

 by Heidenhain and Gaskell on poikilothermic, and by Schmiede- 

 berg, Bowditch. Baxt, Boehm, Franc,ois-Franck, E. Voit, and Eoy 

 and Adanii more particularly on warm-blooded animals. Their 

 results may be summarised as follows : 



Excitation of the accelerators manifests itself after a rather 

 long latent period, which may amount to two seconds. The 

 maximum of acceleration (positive chronotropic effect) first appears 

 after ten or more seconds. The effect of a brief excitation is 

 therefore shown when it is over, as an after-effect. This lasts for 

 a considerable time, exceeding two seconds. The duration of 

 acceleration depends on the length of stimulus, since the accelera- 

 tors are hard to fatigue, even with an excitation lasting for two 

 minutes. 



