SYMPATHETIC VASODILATOR FIBRES

Central and local control. In the course of the Dohme lectures for 1933, Dale contrasted the vasoconstrictor mechanisms of the body with the vasodilator mechanisms, in that the former are for the most part centrally controlled, while the latter are locally controlled. In the introduction to Gaddum’s book, Gefkserweiternde Xto$e der Gewebe, Dale has empha-sised this contrast; he points out that the constrictor regulation is exerted through the vasoconstrictor nerves and also by the liberation of adrenaline or vasopressin, while the dilator regulation is exerted through axon re-flexes at the termination of sensory nerves, or by local liberation of vaso-dilator substances. Apart from centrally controlled dilator nerves to special organs, such as the chorda tympani and the nervi erigentes, Dale concludes that there is no provision for active nervous dilata-tion to satisfy simultaneously the needs of the whole body. According to this view sympathetic vasodilator fibres would be of little functional importance. We could regard their existence as due to an evolutionary error which, had it gone very far, would have rendered useless the sympa-thetic vasoconstrictor fibres; fortunately, however, the error did not de-velop, and the sympathetic vasodilator fibres remained a mechanism hav-ing no more value than the human vermiform appendix. There is, however, another possibility. The view as presented is based in essential points on the physiology of the cat, and it may be unjustifiable to suppose that a system which is simple and logical for that animal is the perfect system for other animals. If our main experimental animal was the mole, a hidebound experimentalist might conclude that the eye was an unimportant sense organ. There is no inherent difficulty in supposing that in larger animals than the cat there is a sympathetic dilator mechan-ism acting nearer the periphery than the main constrictor fibres; through this dilator mechanism, blood supply to muscles (whether skeletal or vis-ceral) can be increased once the constrictor fibres have fulfilled thei