THE CIRCULATION OP THE BLOOD. 



263 



■which, start from the vaso-motor center, descend the cord, and 

 find their way to the organs of a definite region, in consequence 

 of which the muscular coats of the arterioles relax, more hlood 

 flows to this area which is very large, and the general blood- 

 pressure is lowered. 



Again, if the central end of one of the main nerves — e. g., 

 sciatic — ^be stimulated, a marked change in the blood-pressure 



Vasomotor Center 

 in Medulla. 



Spinal Cord. 



Efferent Vaso-mo 

 tor Nerve. 



Ontlying Yasculai 

 Area. 



Afferent Nerve 

 from Periphery. 



i'lG. 219.— Diagram of nervous vaso-motor mechanism. I. Course of afferent impulses 

 from the heart itself along the depressor nerve. II. Course from some other part 

 of the brain. III. Course from some peripheral region along a nerve joining the 

 spinal cord. The efferent impulses are represented as passing to a vascular area, 

 reduced for the sake of simplicity to a single arteriole. 



results, but whether in the direction of rise or fall seems to de- 

 pend upon the condition of the central nervous system, for, with 

 the animal under the influence of chloral, there is a fall ; if 

 under urari, a rise. 



