200 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



interval of many days between the section and the return of arterial tone in areas 

 distal to the section. It has been suggested that during this period the power 

 of the spinal nerve-cell is inhibited by impulses proceeding from the cut sur- 

 face of the cord, 1 but this long inhibition is questionable in view of the fact 

 that transverse section of the cord in rabbits and dogs does not inhibit the 

 phrenic nuclei. 2 



The spinal nerve-cell take- part in vaso-motor reflexes. Thus the stimu- 

 lation of the central end of the brachial nerves after section of the spinal cord 

 at the third vertebra causes a dilatation of the vessels of the fore limb. The 

 stimulation of the central end of the sciatic nerve after the division of the 

 spinal cord causes a general rise of blood-pressure indicating the constriction 

 of many vessels. The sensory stimulation of one hind limb may cause reflexly 

 a narrowing of the vessels in the other, after the spinal cord is severed in the 

 mid-thoracic region. In asphyxia, after the separation of the cord from the 

 brain, vascular constriction is produced reflexly through the spinal centres. 

 This constriction is not observed if the cord is previously destroyed. Goltz 

 and Ewald find that the tonic constriction of the vessels of the hind limbs 

 returns after the extirpation of the lower part of the spinal cord. 



Sympathetic Vaso-motor Centres. — Gley 3 finds that after the destruc- 

 tion of both bulbar and spinal centres some degree of vascular tone is still 

 maintained. The extraordinary experiments of Goltz and Ewald place this 

 fact beyond question. These physiologists remove the lower part of the spinal 

 cord completely, taking away 80 millimeters or more. For a few days after 

 the operation the hind limbs are hot and red, from dilatation of their blood- 

 vessels. Soon, however, the hind limbs become as cool, and sometimes even 

 cooler, than the fore limbs, their arterial tonus being re-established and main- 

 tained without the help of the spinal cord. 



The sympathetic ganglia are probably also centres of reflex vaso-motor 

 action. The fact that these ganglia act as centres for other motor reflexes 

 would itself suggest this possibility. Evidence of the vaso-motor reflex 

 function of the first thoracic ganglion has been offered recently by Francois- 

 Franck. 4 The two branches composing the annulus of Vieussens contain both 

 afferent and efferent fibres. If one of the branches is cut, and the end in con- 

 nection with the first thoracic ganglion is stimulated, the ganglion having been 

 6 sparated from the spinal cord by the section of the communicating branches, 

 a constriction of the vessels of the ear, the submaxillary gland, and the nasal 

 mucous membrane may be observed. 



This evidence, together with the probability that the neuraxons of all the 

 spinal vaso-motor cells end in sympathetic ganglia, 5 makes it fairly credible 

 that the sympathetic vaso-motor nerve-cell possesses central functions. 



1 Goltz and Ewald: Arrhiv fiir die gesammte Physiologie, 1896, lxiii. p. 397. 



'Porter: Journal 'of Physiology, 1895, xvii. p. 459. 



3 Gley: Archives de Physiologic, 1894, p. 704. 



* Franck : Archives de Physiologie, 1894, p. 721. 



5 See the statement of Langley's results with the nicotin method on page '208. 



