Page:The Harveian Oration,1902.djvu/34

26 blood-vessels, no such results occurred in the pulmonary blood-vessels but rather the reverse. This led to the discovery that when the arterioles of organs, otherwise occluded by suprarenal extract, have had their vaso-motor nerves previously paralysed by apocodeine or cocaine, perfusion with suprarenal extract causes dilatation instead of constriction. That this result is not due to paralysis of the muscles of the arterioles is proved by perfusion with chloride of barium, which causes intense constriction and complete stoppage of the outflow. These experiments show, therefore, that supra-renal extract acts by stimulating the nerve-endings of vaso-constrictor nerves, and that there is no evidence of such in the pulmonary blood-vessels.

Generally, it may be said that those organs in which it is necessary for occasional purposes to have an active flow of blood, such as the salivary glands, kidney, and generative organs, are specially provided with vaso-dilators, which sometimes run in separate channels. The centres of the vaso-dilator nerves have not been determined with the same precision as those of the constrictors. It is probable that