The Resonance of the Tissues. 



263 



mm. Hg. mm. Hg. 



Dorsalis pulse disappears at 55. Left radial pulse disappears at 135. 

 „ „ reappears „ 50 „ „ „ reappears „ 130. 



Subject in the horizontal posture. 



In yet another case the pulse disappeared at 35-40 mm. Hg. 



The anterior tibial artery in the leg is overlapped in the upper part of the 

 leg by the tibialis anticus muscle, in the lower part of the leg by the 

 extensor longus digitorum, extensor proprius hallucis, and anterior annular 

 ligament. The dorsalis pedis artery is overlapped by the anterior annular 

 ligament and by the innermost tendon of the extensor brevis digitorum. 

 Consequently, the artery above the point of application of the sphygmo- 

 meter bag is well supported. Yet the readings are similar to readings on 

 positions I and II of the aberrant radial artery. 



The low blood-pressure readings obtained with Hill's pocket sphygmometer 

 on the aberrant radial artery, or on the dorsalis pedis artery, are due to the 

 absence of the resonance of the tissues. Provided one could, in the fore- 

 arm, tie every artery except the radial, and every large branch of the 

 radial artery, one would find then that the blood-pressure readings taken 

 by Hill's pocket sphygmometer, or by the armlet method, would approxi- 

 mate closely to the low readings found in the aberrant radial artery. 



Another method of demonstrating the effect of resonance on the pulse 

 is the following : — Blood-pressure readings are taken in an individual in 

 the upright position, from the forearm held at the level of the heart. 

 The systolic blood-pressure is found to be 120 mm. of Hg (disappearing 

 pulse index). A similar reading is found in the other arm. One arm is 

 then fully extended above the head, and the forearm, from the tips of the 

 fingers to the elbow, is bandaged tightly to render the limb ischsemic. 

 An armlet is fitted to the upper arm, and the pressure is raised 

 in it well above the systolic pressure to prevent the blood flowing into 

 the ischemic limb. The bandage is then removed, and the arm lowered 

 to the heart level. Hill's pocket sphygmometer is now placed on the 

 forearm covering the same position as before (the position is previously 

 outlined with ink) and the radial artery is blocked with one finger to 

 prevent a pulse from the ulnar recurrent artery ; the pressure in the armlet 

 is then let down rapidly by pulling the tube off the metal connection of 

 the compressing bulb. When the first pulses are felt at the wrist, the 

 bag of the sphygmometer is pressed on to the artery until the pulse is 

 damped down, a pressure of 70 mm. of Hg suffices to do this. Soon the 

 pulse reappears below the bag, and the bag has to be pressed on with, say, a 



