550 THE OUTGO OF ENERGY 



inhale two drops (on no account more than two) 

 of the nitrite of amyl (to be dropped on a hand- 

 kerchief by one of the instructors). This power- 

 ful drug causes dilatation of the blood vessels, 

 particularly the smaller arteries. 



Observe that as the face flushes, indicating the 

 vascular dilatation, the pulse will be softer. 



Do not repeat the experiment. 



Pressure-Pulse in Aortic Regurgitation. Empty 

 the principal tubes of the artificial scheme. Re- 

 move the rubber from about the aortic valve. 

 Replace the valve tube. Fill the apparatus with 

 water. Revolve the disk at the rate and with 

 the force employed to imitate the normal circula- 

 tion (page 545). 



Feel the pulse with the finger. 



After each systole the liquid streams back 

 through the incompetent valve. The ventricle 

 is thus fuller than normal at the beginning of 

 the stroke, while the arteries are less than 

 normally full. Consequently more than the 

 usual quantity is discharged by the ventricle 

 into relatively undistended arteries. The rela- 

 tively lax artery is thereby quickly and largely 

 expanded, as indicated by the quick thrust given 

 the palpating finger and by the large excursion 

 of the mercury in the arterial manometer. 



Record pulse curves. 



