THE CIRCULATION 145 



as some do, that the actual 4 ounces or so of blood 

 which is expelled at any given systole rushes straight 

 along the arteries and produces a ' swelling of them,' 

 and that this is the pulse, is erroneous, though it may 

 be admitted that such a misconception need not make 

 a man a worse physician. On the other hand, one can 

 hardly feel a pulse intelligently unless it be clearly 

 realized that it indicates merely a change in shape of 

 an artery from an oval to a circular form along with 

 a certain amount of straightening out, like a slack wire 

 suddenly put on the stretch and not a real increase in 

 circumference of the artery (Fig. 7). The proof of this, 



FIG. 7. SHOWING THE CHANGE IN SHAPE OF AN ARTERY FROM 



AN OVAL TO A CIRCULAR FORM DURING THE PASSAGE OF 



THE PULSE WAVE. 



as Broadbent pointed out, is readily demonstrated by 

 placing the foot on a leather fire-hose (which of course 

 cannot change in calibre), when a pulse will be felt at 

 each stroke of the pump. 



Of the characters of the pulse studied at the bedside, 

 one group its frequency, regularity, and equality are 

 entirely cardiac in origin, and are merely convenient 

 indications of the way in which the systole is being 

 performed. 



Of these features the frequency need alone be referred 

 to here, as variations in regularity and equality have 

 been dealt with in considering the heart. 



10 



