542 CIRCULATION OF BLOOD AND LYMPH. 



clearly that the vasoconstrictor center is easily affected in a pressor 

 or depressor manner by psychical states or activities. Mental 

 work, especially mental interest, however aroused, is followed by 

 a constriction of the blood-vessels of the skin, a pressor effect (see 

 Fig. 225) ; and we may find an explanation of the value of the reflex 

 in the supposition that the rise of arterial pressure thus produced 



Fig. 226. Effect of stimulating the central end of the depressor nerve of the heart. 

 (Dawson.) The time record marks seconds. On and off mark the beginning and end of 

 the stimulation. The blood-pressure rises slowly after the removal of the stimulus and 

 eventually reaches the normal level. This complete recovery is not shown in the por- 

 tion of the record reproduced. 



forces more blood through the brain (p. 560). On the other hand, 

 feelings of embarrassment or shame may be associated with a de- 

 pressor effect, a dilatation in the vessels of the skin manifested, for 

 example, in the act of blushing. In both cases we must assume 

 intracentral nerve paths between the cortex and the center in the 

 medulla, the impulses along one path exciting the center, while 

 those along the other inhibit its tone, or, as explained below, excite 



