III. The innervation of the pulmonary vessels

Although hitherto most physiologists have considered that the pulmonary vessels probably possessed a system of vaso-motor nerves, yet no direct experimental proof of the existence of such a system has been obtained. Still less has any evidence been adduced to demonstrate the actual anatomical paths by which such nerves, if they exist, reach the lungs. Hence it seemed that the whole question was one deserving a further attempt for its solution. When this research was commenced, there were practically only two facts which could be appealed to in support of the existence of these nerves.