HuBER, Innervation of the Intracranial Vessels. 23 



of the literature bearing on this subject. Before concluding this 

 paper it may, however, not be amiss to state briefly what may 

 be regarded as the consensus of the opinions of physiologists 

 on the question of the vaso-motor nerve supply of the intra- 

 cranial vessels, and in doing this I quote from Hill, whose ex- 

 tended observation and knowledge of the literature enable him 

 to make such a summary much better than I can. 



" No evidence has been found of the existence of cerebral 

 vaso-motor nerves : either by means of stimulation of the vaso- 

 motor center, or central end of the spinal cord after division of 

 the cord in the upper dorsal region : or by stimulating the stel- 

 late ganglion, and, that is to say, the whole sympathetic supply 

 to the carotid and vertebral arteries." "In every experimental 

 condition the cerebral circulation passively follows the changes 

 in the general arterial and venous pressures." " There is no 

 compensatory mechanism by which the intracranial pressure is 

 kept constant." And to quote still further. Hill states that in 

 "turning to the evidence of past workers, I find that Nothnagel 

 and Akermann obtained at times, on stimulating the cervical 

 sympathetic, evidence of dilatation of the pial vessels. Recently 

 Cavazzani found evidence of both cerebral constrictor and dila- 

 tor fibers in this nerve; the methods of these workers are value- 

 less in deciding such a question. Schultz, Riegel and Jolly, 

 Cramer, v. Schulten, Gaertner and Wagner, Hiirthle, Roy and 

 Sherrington have obtained no positive evidence of any active 

 cerebral effect from stimulation of this nerve." In this con- 

 nection it may be interesting to note that Hill states that " in a 

 recent exhaustive research, Gulland has failed to demonstrate 

 by every known histological means the existence of any vaso- 

 motor nerves in the pial vessels." This latter statement at least 

 needs modification, since, as has previously been shown Gulland 

 himself admits the presence of perivascular nerves on the pial 

 vessels. 



The statement above made may serve to emphasize the 

 view previously expressed, that physiologists very generally 

 deny the existence of vaso-motor nerves in the pial vessels. 

 The fact that nerves, which in every respect — considered struc- 



