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A TEXTBOOK OF PHYSIOLOGY 



in this case the effect must be brought about by active excitation of 

 the vaso-dilator nerves. It is probable that there arc vaso-dilator 

 fibres in sympathetic nerves. Thus adrenalin, which normally causes 

 a rise of arterial pressure, after a dose of ergotoxine causes a fall 

 (Fig. 121). The best explanation of this result is that vaso-dilator 

 fibres are now stimulated. It seems probable that with depressor 

 reflexes there is, along with the inhibition of tone in the vaso-constrictor 

 centre, an excitation of the vaso-dilator centre; and with pressor 

 reflexes an excitation of the vaso-constrictor centre and an inhibition 

 of the vaso-dilator centre (Fig. 122). When an afferent nerve from 



FIG. 125. THE EFFECT OF THE SUGGESTION TO A HYPNOTIZED SUBJECT OF HIS 

 EXECUTION (- TO +) UPON (1) THE VOLUME OF THE ABDOMINAL ORGANS, 

 (2) THE VOLUME OF THE AKM, (3) THE RESPIRATION. 



any particular organ e.g., the kidnej- (Fig. 123) excites the usual 

 pressor reflex on the general blood -pressure, a vaso-dilatation is pro- 

 duced through spinal centres in the organ itself, thus ensuring a 

 maximal blood supplj" to the active organ. In these local reflexes 

 there is excitation of constrictors and inhibition of vaso-dilators 

 (Fig. 123). That these reflex vaso-motor effects frequently occur is 

 shown by the blush of shame, the blanching of the face by fear, the 

 blanching of the skin by cold, and the, flushing which is produced by 

 heat. The rabbit's ear blanches if its feet arc put into cold water. 

 In Fig. 124 are shown the effects of pleasant KnA vnaptcasant tastes 



