260 Messrs. L. Hill, J. M. McQueen, and W. W. Ingram. 



It is to be noted that the same length of artery is under pressure in both 

 cases. The bags are covered with the hand in a precisely similar manner, 

 yet the pulse at a reappears at 90 mm. ; at b, reappears at 60 mm. 



This difference can be explained by an analysis of the tissues underlying 

 the bag in either position. In position a, 2/3 of the bag lies on the fleshy 

 belly of the supinator longus and biceps, and over the arterial anastomosis of 

 .the radial recurrent artery and the superior profunda artery. In position b, 

 2/3 of -the bag lies on the tendinous insertions of the flexor group of 

 muscles. Here the arterial supply is much less. Consequently, the 

 resonance of the tissues in position a is greater than the resonance of the 

 tissues in position b, and the pulse suffers a great damping-down in 

 position b. 



Here we have no question of loss of pressure through overlying or 

 distorting tissues. The tissues over the artery are the same in both cases. 

 The pressure on each point of the circumference of the bag is the same. 

 Consequently, it must be that, in position a, the air delivering the pressure 

 is in a state of greater periodic vibration than the air in the bag in position b. 

 The vibrations that underlie the phenomenon of sound are transmitted in 

 water as in air. "We find that when water is substituted in the bag for air 

 the same results are obtained. The water takes on the periodic vibrations of 

 the resonating tissues. 



L. Hill and Eussell Wells (2) have recently shown how important 

 a factor in the pulse curve is the lability of the arterial wall. It has 

 also been shown by L. Hill and Martin Flack (3) that, when an artery is 

 freed from the tissues, and thereby deprived of the support of the tissues 

 round its wall, the pulse curve is much affected. The lability of the wall is 

 called into play, and the systolic pressure of the heart is spent in distending 

 the wall of the artery. It was possible, then, that the artery lying more or 

 less superficially at positions II, III, and IV, would have its wall distended, 

 so that the pulse arriving under the bag at position I would be already 

 damped down before pressure was applied to the artery at position I. 



Our experiments show that, at position I, with a pressure, say, of 

 60 mm. of Hg, the pulse is skimmed off the blood current, but the arterial 

 flow remains. Consequently, the block on the blood flow is not an 

 absolute one. 



Experiments were made by supporting the superficial artery with the 

 armlet and with the bag of another sphygmometer, to determine whether 

 such support played any part in the production of the low pressure reading 

 at position I. 



Our results show that no matter what pressure is raised in the armlet on 



