CIRCULATION 31 



diminished. If now several small tubes unite to form one, 

 and this is joined by another formed in the same way and 

 the process is repeated until there is but one tube, the 

 pressure in that will be less than the pressure in the 

 numerous microscopic tubes, and much lower than it 

 was in the one large elastic tube because friction so 



Fig. 7. Apparatus for measuring the arterial blood pressure in man. The 

 pressure in the cuff is raised by means of the syringe until the pulse can 

 no longer be felt at the wrist. This pressure is read off on the mercury 

 manometer (systolic pressure). (Pearce-Macleod, Fundamentals of Hitman 

 Physiology.) 



retards the flow that the larger tube can never be filled. 

 The arteries, capillaries, and veins form such a set of 

 tubes and blood pressure varies in these sets of vessels. 



