1102 PHYSIOLOGY 



similar, though more rapid, accommodation of this organ is to be seen 

 whenever there is a sudden rise of blood pressure. Thus if the pressure 

 be quickly raised by clamping the descending aorta or by stimulation 

 of the splanchnic nerves, the ventricles at first dilate, so that their 

 systolic volume increases for a little time, while the blood pressure is 

 rising. As a result the blood pressure ceases to rise, but at this point 

 the ventricle muscle seems to gather renewed strength, the systolic 

 volume diminishes, and the output at each beat increases, so that 

 the blood pressure rises still further and the heart continues to contract 

 at the higher level of blood-pressure as efficiently as it did before the 

 pressure began to rise. On this account the curve of blood pressure 

 is generally ' stepped.' Such a curve with the accompanying changes 

 in the heart volume is shown in Fig. 456. 



