Page:The Harveian Oration,1902.djvu/44

 —practically the whole of the sympathetic supply to the carotid and vertebral arteries—or even, according to Hill, of the central end of the cut spinal cord or the vaso-motor centre itself. The opposite results obtained by Nothnagel, Cavazzani, and others are attributable to defective methods of experiment, which do not differentiate between active and passive variations in the calibre of the vessels, or exclude changes due to mere atmospheric exposure. This negation of vaso-motor regulation of the cerebral blood-vessels seems to be in flagrant contradiction with the positive demonstration of nerves accompanying the vessels of the pia mater, as well as with other facts, such as the apparently independent variations of the plethysmographic volume records described by Mosso, and we can scarcely doubt that there must be some intrinsic mechanism which can secure a greater flush of blood in one part as compared with another in an organ in which there is proved localisation of function. Roy and Sherrington believed that they had discovered such a mechanism in the products of cerebral meta-