THE CIRCULATION OF THE BLOOD 515 



Normal sphygmographic tracings may be obtained 

 by using a sphygraograph on the aortic tube. 



Palpation of the arterial tube will give a pulse the 

 "feel" of which cannot be distinguished from that of 

 the pulse in the normal subject ; the pressure waves 

 in the quantitative scheme and in the living animal 

 are identical in respect of both time and pressure. 



THE CONVERSION OF THE INTERMITTENT INTO A 

 CONTINUOUS FLOW 



When a pump forces water or any other 

 incompressible fluid through tubes with rigid 

 walls, the inflow and outflow are equal and in the 

 same time. The outflow ceases the instant the 

 inflow ceases. The same is true in a system of 

 elastic tubes so short and wide that friction be- 

 tween the liquid and the walls causes practically 

 no resistance to the flow. Here the quantity 

 received from the pump can still escape from the 

 distal end of the system during the stroke of the 

 pump. When the resistance is increased by 

 narrowing the tubes, or by increasing their 

 length, or in both these ways, not all the liquid 

 received from the pump can pass by the resist-) 

 ance during the stroke of the pump, the re- 

 mainder must pass during the interval between 

 one stroke and the next. The portion which 

 cannot pass during the stroke finds room be- 



