204 AN AMERICAN TEXT- BOOK OF PHYSIOLOGY. 



into account many sources of error that are absent in vaso-motor studies of 

 other regions. It is, indeed, probable that incompleteness of method will go 

 far Toward explaining the disagreement of authors as to the presence of vaso- 

 motor nerves in the brain. According to Bayliss and Hill, who have recently 

 studied this subject, it is necessary to record simultaneously the arterial 

 pressure, the general venous pressure, the intracranial pressure and the cerebral 

 venous pressure, the cranium as in the normal condition being kept a closed 

 cavity. In their experiments, "a cannula was placed in the central end of the 

 carotid artery. A second long cannula was passed down the external jugular 

 vein, and on the same side, into the right auricle. The torcular Herophili was 

 trephined, and a third cannula, this time of brass, was screwed into the hole 

 thus made." The intracranial pressure was recorded by a cannula connected 

 through another trephine-hole with the subdural space. 



Bayliss and Hill could find no evidence of the existence of cerebral vaso- 

 motor nerves. The cerebral circulation, according to them, passively follows 

 the changes in the general arterial and venous pressure. Gulland has examined 

 the cerebral vessels by the Golgi, Ehrlich, and other methods, to determine 

 whether nerve-fibres could be demonstrated in them. None were found. It 

 is probable that the blood-supply to the brain is regnlated through the bulbar 

 va-n-eonstrictor centre. Anaemia or asphyxia of the brain stimulates the cells 

 composing this centre, vascular constriction of many vessels follows, and more 

 blood enters the cranial cavity. The vessels of the splanchnic area play a 

 chief part in this regulative process. 1 Their importance to the circulation in 

 the brain is shown by the fatal effect of the section of the splanchnic nerves 

 in the rabbit. On placing the animal on its feet, so much blood flows 

 into the relaxed abdominal vessels that death may follow from anaemia of the 

 brain. 



Vaso-motor Nerves of Head. — The cervical sympathetic contains vaso-con- 

 strictor fibres for the corresponding side of the face, the eye, ear, salivary 

 glands and tongue, and possibly the brain. The spinal vaso-constrictor 

 fibres tor the vessels of the head in the cat and dog leave the cord in the 

 first five thoracic nerves ; in the rabbit, in the second to eighth thoracic, seven 

 in all. 



Vaso-dilator fibres for the face and month have been found in the cervical 

 sympathetic by Dastre and Morat, leaving the cord in the second to tilth 

 dorsal nerves, and uniting (at least for the most part) with the trigeminus by 

 passing, according to Morat, from the superior cervical >yinpathetic ganglion 

 to the ganglion of Gasser. Other dilator fibres for the skin and mucous 

 membrane of the face and mouth arise apparently in the trigeminus, for the 

 stimulation of this nerve between the brain and Gasser's ganglion causes dila- 

 tation of the vessels of the face, 2 and in the nerve of Wrisberg. 



The vaso-motor nerves of the tongue have been recently studied by Isergin. 3 



1 Wertheiiner : Archives de Physiologic, 1893, p. 297. 



2 Langley: Philosophical Transactions, 1892, j). 104 ; Piotrowsky : Ccntralblatt fiir Physiologic 

 1892, vi. p. 464. 3 Isergin : Archie fiir Physiologic, 1894, p. 441. 



