572 



PHYSIOLOGY 



CHAP. 



pressure, followed by a regular drop to the normal, and even below 

 it. The pressure curve is comparable with that obtained under 

 identical conditions of suppression of moderating influences, on 

 direct or reflex excitation of the bulbo-spirial centres. Only very 

 rarely does cortical excitation produce a depressor effect due to 

 vascular dilatation; it is probable that the brain may produce 

 active dilatation of limited vascular regions, and does not sensibly 

 affect the general arterial pressure. 



These vascular changes due to cortical excitation are not 



FIG. 292. Opposite effect upon volume of kidney (Vol.R.) and arterial pressure (P.O.) of cortical 

 excitation (shown on lower line). (Francois-Franck and Pitres.) Arterial pressure rises from 

 130 to 260 mm. Hg., while the volume of the kidney diminishes. As the animal was atropinised, 

 the excitation does not affect cardiac rhythm, and the pressor effect in this case evidently 

 depends on the contraction of the vessels, both superficial and deep or visceral. 



elicited from the whole of the brain surface ; unless very strong 

 currents capable of producing epileptic attacks are used, fara- 

 disation of the anterior frontal, inferior lateral, and posterior 

 occipital regions are ineffective. Vaso-motor effects are constant 

 on stimulating the motor area; whatever point of this region 

 is excited the vasomotor reaction is general and bilateral; it is 

 not more pronounced in the limb that corresponds with the centre 

 excited, nor in the superficial than in the deep vessels (Fig. 292). 

 It is probable that vascular response can be produced from the 

 excitable area of the cortex in proportion as this contains afferent 

 paths to the vasomotor centres of the bulb ; the vascular reactions 



