322 THE NERVOUS REGULATION OF THE HEART 



pressure.^ These changes prove very clearly that the stoppage of 

 this organ is followed by a gradual transfer of the arterial blood into 

 the central veins, right auricle and ventricle. We obtain, therefore, a 

 condition very similar to that found at death, when the recoilirng ar- 

 teries force the blood into the venous collecting channels. The 

 arterial blood pressure rises again with the return of the cardiac con- 

 tractions. The venous pressure drops proportionately. It is to be 

 noted, however, that the systoles occurring directly after the inhibition 

 cause more decided changes than those taking place later on, because 

 the gradual refilhng of the arterial system and returning tension must 

 necessarily lead to a corresponding diminution of the systolic-diastohc 

 difference in pressure. When the cardiac output has again become 

 normal, the pressures assume their former level. In most cases. 



Fig. 170. — Record op Carotid Blood-pressure. 

 S, stimulation of left vagus nerve. The fall in pressure is followed by compensatory 

 changes before the normal pressure is again established. 



however, the arterial pressure does not become constant until it has 

 first risen somewhat above its normal value. In fact, this initial 

 rise above normal is frequently followed by a fall below normal. 

 These oscillations, occurring in the wake of the inhibition, are depend- 

 ent upon the attempt on the part of the arterial system to compensate 

 for the loss in pressure. To begin with, the arteries constrict more and 

 more, as the blood leaves them to enter the veins. In this condition, 

 they remain until the first ventricular discharge subsequent to the 

 inhibition again distends them. The resistance thus placed in the path 

 of the successive cardiac outputs tends to raise the pressure rather 

 abruptly so that its normal value is temporarily exceeded. At this 

 very moment the vasoconstriction gives way to a vasodilatation with 



1 Burton-Opitz, Am. Jour, of Physiol., ix, 1903. 198. 



