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



II, while the bag is pressed on part of II and part of I, the following reading- 

 can then be taken : — 



Here there can be no question that the blood flow passes through the 

 pressure of 90 mm. of Hg, and therefore cannot be arrested by a pressure 

 of a bag at 55 mm. of Hg. A further possibility suggests itself that the 

 pulse may be diverted through pressure on the bag, and seek an easier 

 channel through some branch of the radial artery. Against this supposition 

 we suggest : first, that the branch chosen must be a big one, otherwise what 

 the pulse gains in an easier path is lost in the friction due to the narrower 

 lumen ; second, that a pulse would never pass back from the bag at 50 mm. 

 of Hg, under the armlet at 90 mm. of Hg. Consequently we conclude that 

 with the bag in position I the pulse is damped down under the bag, while 

 there is but a trifling obstruction to the blood flow in the artery. The 

 blood in the artery below the bag takes on the characters of a venous 

 flow. 



The aberrant radial artery where it lies in part of position I, in position II, 

 and position III was covered by the armlet, and while preventing the 

 recurrent ulnar pulsation, a reading was taken. The pulse was then found 

 to disappear and reappear between the limits of 120-130 mm. of Hg. Con- 

 sequently the aberrant radial artery in positions I and II, overlying bone 

 ligaments and tendons, can withstand a pressure of, say, 110 mm. of Hg without 

 the pulse being damped down. But with the bag of the pocket sphygmo- 

 meter at position I or at position II, the pulse is removed from the blood 

 current with a pressure of 55-60 mm. of Hg. Yet, according to physical 

 laws, the pressure is equally delivered to the elastic wall of the artery 

 by both instruments. The problem is seen then to depend on the air 

 contained in the armlet in the one case,, and on the air contained in the 

 bag in the other. It is not a matter solely of pressure in the air of the 

 armlet or of the bag, but the important factor is the state of the air in both 

 cases as regards periodic vibrations. 



The air in the armlet is in a state of periodic vibration. These 

 vibrations depend on the pulsation of the mass of tissues which surround 

 the ulna and radius and are embraced by the armlet. At every beat 

 of the heart the incompressible blood is pumped into the tissues through 

 arteries large and small, and the pulse of each and every artery is 

 directed as much outwards into the tissues as inwards upon the blood 

 stream. Consequently the tissues become a pulsating mass, as can be 



Pressure in armlet 



Pulse disappears below bag at 



rum. of Hg. 



90 



55 



