694 



PRINCIPLES OF GENERAL PHYSIOLOd'Y 



It has long been known that there is a particular part of the bulb which ;u-ts 

 as centre for the former, although it is probable that wluit is called the " vasonmt or 

 centre " is rather a nerve tract containing fibres from scattered centres. The 

 vaso-dilator centre has not yet been localised. 



It is evident, then, that reflex vaso-constriction or dilatation might each be 



Fu;. 242. Similar experiment to that of Fig. 241, hut on the rabbit, 

 the central end of the depressor nerve itself being stimulated. 



There is very little fall of blood pressure, owing to the use of a mercury 

 compensating arrangement. 



(Bayliss, 1908, 3, Fig. 7.) 



produced in two ways ; the former, either by excitation of the constrictor centre 

 or by inhibition of tone in the dilator centre, supposing such tone to be present ; 



VASCTLAK DILATATION i\ THK HIND LIMP. HV KXI ITATION 

 OK DILATORS. Abdominal sympathetic cut. 



n, Volume of hind lejr of i\og. 



A, Arterial pressure. 



p, signal marking stimulation of central end vajrtis. 



B, Time in seconds. 



Coincident with the fall in arterial pressure, due to the depre-^n- film-* in the vajrus, 

 there is dilatation of the limh, althoujrh there were no vaso-constrictors whose 



tone could he inhibited. 



(Fofanov und Chalussov.) 



the latter, by excitation of the dilator centre, or by inhibition of tone of the 

 constrictor centre, supposing it to be in a state of tonic excitation. 



In early work on vascular reflexes, the existence of vaso-dilator nerves was 

 not taken account of, so that^the peripheral dilatation produced from the depressor 

 nerve was ascribed by Cyon and Ludwig to inhibition of the constrictor centre. 



