VASO-DILATOR NERVES 85 



from the cord between the first dorsal and third lumbar 

 segments, that the fibres which supply the abdominal and 

 pelvic viscera pass, without interruption, through the 

 sympathetic chain and have cell-stations in the collateral 

 gangha — the semilunar, superior and inferior mesenteric 

 gangha, and that fibres which supply the blood-vessels of 

 the skin have cell-stations in the sympathetic chain from 

 which post-ganglionic fibres emerge and travel to the 

 periphery bound up in the ordinary nerve-trunks. 



There appears to be no vaso-motor control over the 

 arteries of the brain or the coronary arteries of the heart. 

 In the pulmonary vessels vaso-motor influence is indicated 

 by the constriction which occurs on the administration of 

 adrenalin. 



When a vaso-constrictor nerve is stimulated it will 

 produce a double effect — first, a diminution in the blood- 

 supply to the part of the body to which it is distributed ; 

 secondly, if the distribution of the nerve is sufficiently 

 extensive, stimulation will, by diminishing the outflow from 

 the arteries, tend to raise the general blood-pressure. 



Vaso-dilator Nerves 



Claude Bernard showed that the chorda tympani nerve 

 on stimulation caused dilatation of the blood-vessels to 

 the submaxillary gland, and that this occurred indepen- 

 dently of secretion. This was the first demonstration that 

 there exist nerves which on stimulation cause an inhibition 

 of the tonus of the vessels. Vaso-dilator fibres occur also 

 in the nervus erigens supplying the penis. In both these 

 cases the vaso-dilator effect is sufficiently striking to 

 warrant our beheving the existence of nerves having this 

 special function. 



When we turn to the blood-vessels in general we find 

 ourselves on more debatable ground. Do the sympathetic 

 nerves convey vaso-dilator as well as vaso-constrictor 

 impulses? The only positive information we have on 



