168 



AN AMERICAN TEXT- HOOK OF PHYSIOLOGY. 



accompanying this rise in blood-pressure would alone explain the observation 

 of von Bezold. Three years later Bever and von Bezold were more suc- 

 cessful. The influence of the vaso-motor nerves was excluded by section of 

 the spinal cord between the first and second thoracic vertebrae. Stimulation 

 of the cervical cord now caused an increase in the frequency of the heart-beat 

 without a simultaneous increase of blood-pressure. The fibres carrying the 

 accelerating impulse were traced from the spinal cord to the last cervical gan- 

 glioD and from there toward the heart. 



In the dog the " augmenting " or " accelerating " nerves thus discovered 

 leave the spinal cord mainly by the roots of the second dorsal nerves, and enter 

 the ganglion stellatum, whence they pass through the anterior and posterior 

 loops of the annulus of Vieussens into the inferior cervical ganglion, from 

 which they go, in the cardiac branches of the latter, to the heart. Some of 

 the cardiac fibres in the annulus pass directly thence to the cardiac plexus and 

 do not enter the inferior cervical ganglion. 



In the rabbit, the course of the augmentor fibres is probably closely similar 

 to that in the dog. 



In the cat, the augmentor nerves spring from the ganglion stellatum, and 

 very rarely from the inferior cervical ganglion as well. The right cardiac 

 sympathetic nerve communicates with the vagus. 



The stimulation of the sympathetic chain in the frog, " between ganglion 1 

 and the vagus ganglion, and also stimulation of the chain between ganglia 2 



and 3, causes marked acceleration and 

 augmentation of the auricular and ven- 

 tricular contractions. Stimulation be- 

 tween ganglia 3 and 4 produces no effect 

 whatever upon the heart." This ex- 

 periment of Gaskell and Gadow's shows 

 that augmentor fibres enter the sympa- 

 thetic from the spinal cord along the 

 ramus communicans of the third spinal 

 nerve and pass upward in the sympa- 

 thetic chain. In this animal the sym- 

 pathetic chain, after dividing between 

 the first and second ganglia to form the 

 annulus of Vieussens, joins the trunk 

 of the vagus between the united vagus 

 and glosso-pharyngeal ganglia and the 

 vertebral column (see Fig. 33). Here the sympathetic again divides, some of 

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

 in- the vagus nerve peripherally. The augmentor nerve- for the heart are 

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

 inhibition, 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 



V-Sy 



Fig. 33.— The cardiac sympathetic nervt- in 



Rana temporalis (twice natural size): V-Sy, 



mpathetic; A.v, arteria vertebralis; II, 



TV, second and fourth spinal nerves (.Gaskell 



ami Oa.low, lsMj. 



