INHIBITORY NERVES TO THE VASCULAR SYSTEM 93 



of degeneration and of slow rhythmical stimulation. The vaso- 

 dilators are held to resist degeneration longer than the vaso- 

 constrictors, and can be excited by a weaker stimulus. In all the 

 instances considered previously, namely of the vascular supply 

 to muscles or glands, the marked characteristic has been that the 

 so-called vaso-dilator nerves arise quite differently from the vaso- 

 constrictor nerves, and have no connexion with the sympathetic 

 system. 



The evidence for vaso-dilator fibres in the sympathetic 

 was given in the first instance by the observations of Dastre 

 and Morat, which have been confirmed by Heidenhain and 

 Langley. The former found that, while stimulation of the 

 cervical sympathetic caused constriction of blood vessels over 

 the head and face region, it caused at the same time a marked 

 flushing inside the mouth and gums which was very visible 

 in dogs and could be easily observed in white dogs ; this 

 bucco-facial dilatation was ascribed by them to the action 

 of vaso-dilator nerves to these parts, which ran in the cervi- 

 cal sympathetic. No particular kind of stimulation was re- 

 quired and the phenomenon occurred with the freshly cut 

 nerve. Neither Dastre, Morat, Heidenhain, or Langley have at- 

 tempted to decide what part glandular secretion may play in 

 this phenomenon. The places where the flushing has been ob- 

 served are well supplied with glands, which are almost certainly 

 supplied with secretory fibres from the cervical sympathetic. It 

 is therefore more probable than not, that the flushing observed 

 is explainable by the action of metabolites due to such secretion 

 rather than as a result of stimulation of vaso-dilator nerves. 



Secondly, the sympathetic may carry vaso-dilator nerves for 

 the kidney. These nerves have been investigated by Bradford. 

 He examined the roots of the thoracic and lumbar nerves, and 

 found that stimulation of the posterior roots produced no effect 

 on the kidney, but that constriction of its vessels with a rise of 

 blood pressure was manifest on stimulation of the anterior nerve 

 roots of the sixth thoracic to the first lumbar nerves in the dog 

 (enumerating here seven lumbar nerves). The anterior roots of 

 the eleventh, twelfth and thirteenth thoracic contained the main 

 mass of renal vaso-constrictor nerves. He found further that when 

 those same nerve roots were stimulated with a slow rhythmical 

 stimulation (one shock per second), then instead of constriction a 



