460 



AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



the fibres passing alongside the vagus into the cranial cavity, the rest accompany- 

 ing the vagus nerve peripherally. The augmentor nerves for the heart are 

 among the latter, for the stimulation of the intracranial vagus results in pure 

 inhibition, 1 while the stimulation of the vagus trunk after it is joined by the 

 sympathetic may give either inhibition or augmentation. We may say, there- 

 fore, that the augmentor nerves of the frog pass out of the spinal cord by the 

 third spinal nerve, through the ramus communicans of this nerve, into the 

 third sympathetic ganglion, up the sympathetic chain to the ganglion of the 

 vagus, and down the vagus trunk to the heart. 



Stimulation of Augmentor Nerves. The most obvious effect of the stim- 

 ulation of the augmentor nerves is an increase of from 7 to 70 per cent, in the 

 frequency of the heart-beat (see Fig. 119). The quicker the heart is beating 

 before the stimulation, the less marked is the acceleration. The absolute maxi- 



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," 21 J- 28 



FIG. 119. Curve of blood-pressure in the cat, recorded by a mercury manometer, showing the 

 increase in frequency of heart-beat from excitation of the augmentor nerves. The curve reads from 

 right to left. The augmeutor nerves were excited during thirty seconds, between the two stars. The 

 number of beats per ten seconds rose from 24 to 33 (Boehm, 1875, p. 258). 



mum of frequency is, however, independent of the frequency before stimulation. 2 

 The maximum of acceleration is largely independent of the duration of stimula- 

 tion. The duration of stimulation and the duration of acceleration are not 

 related, a long stimulation causing no greater acceleration than a short one. 3 



The force of the ventricular beat is increased.* The ventricle is filled more 

 completely by the auricles, the volume of the ventricle being increased. The 



FIG. 120. Increase in the force of the ventricular contraction (curve of pressure in right ventricle) from 

 stimulation of angmentor fibres. There is little or no change in frequency (Franck, 1890, p. 819). 



output of the heart is raised. 5 There is no definite relation between the in- 

 crease of contraction volume or force of contraction and the increase in fre- 

 quency (see Fig. 120). Either may appear without the other, though this is 



1 Gaskell, 1884, p. 48. z Boehm, 1875, p. 277. 3 Baxt, 1877, p. 523. 



* Heidenhain, 1882, p. 396; Gaskell, 1884, p. 47; 1886, p. 42; Mills, 1886, p. 554; Franck, 

 1890, p. 814; Roy and Adami, 1892, p. 242; Bayliss and Starling, 1892, p. 413. 

 5 Roy and Adami, 1892, p. 240. 



