ADVANCED EXPERIMENTAL PHYSIOLOGY 351 



(3) The vagus is the inhibitory nerve to the heart, the motor nerve 

 to the bronchial muscles. 



It conveys both inhibitory and augmentory impulses to the 

 alimentary canal. 



It is a secretory nerve to the gastric glands and pancreas. 



It contains afferent fibres from* the heart which provoke reflex 

 movements, pressor or depressor effects, and reflex cardiac inhibition. 



The afferent fibres of the vagus coming from the lungs regulate the 

 rhythm of respiration. 



The superior laryngeal branch of the vagus is the motor nerve to 

 the crico-thyroid muscles and the sensory to the larynx. 



The inferior laryngeal branch is the motor nerve to the intrinsic 

 muscles of the larynx. 



CHAPTEE XXVI. 

 THE PULSE. 



The Velocity of Transmission of the Pulse Wave. Two tambour 

 sphygmographs are taken, and one is applied to the carotid, and the 

 other to the radial or femoral artery. The recording tambours are 

 brought to write exactly beneath one another on a fast drum, and a 

 time tracing is taken with the tuning fork. The distance between the 

 carotid artery and the radial or femoral is measured. The rate of 

 transmission is about 5-8 metres a second. The rate of transmission 

 increases as the coefficient of elasticity of the arterial wall. It is 

 therefore greater with high than with low arterial pressure. 



The velocity of transmission from carotid to radial may be lessened 

 by placing the arm in water so as to produce vaso-dilatation. During 

 the first six beats after vagus arrest of the heart, the velocity of 

 transmission was 4 -5, 4 -5, 6'0, 7 '5, 12, 13 -5 metres per second re- 

 spectively. The length of the pulse wave is the product of the 

 velocity of transmission by the time occupied by the wave in passing 

 any given point. Calculate this value from the record. It is about 

 5 metres, so the pulse wave reaches the periphery before it has left 

 the aorta. 



Impulse and Pulse Curves. The cardiac impulse and the carotid 

 pulse may be simultaneously recorded in man, and by this means the 

 time relations of the cardiac cycle may be determined. The carotid 

 pulse is recorded by means of a receiving tambour, which is strapped 

 round the neck, and is provided with a button which rests on the 



