The. Resonance of the Tissues. 



267 



tense with blood and does not vibrate strongly with the pulse, consequently 

 the sphygmometer bag acts as a damper. The rise of the pulse to maximal 

 is aided by the resonance of the tissues. But whether the pulse beat is 

 maximal or not it is bound to surfer clamping down so long as the resonance 

 of the surrounding tissues is feeble. 



It will be noted that the blood pressure in the cold ischsemic limb returns 

 much more slowly to normal than in the warm ischsemic limb. Here the 

 arterioles of the limb are contracted ; consequently the blood takes longer 

 to percolate into the ischsemic tissues, the drum-head takes longer to tighten 

 up, and the resonating effect consequently longer to develop. After dilatation 

 has been produced in the vessels of a limb, repeatedly made ischsemic, it is 

 less easy to obtain the staircase effect. The bandaging has then to be done 

 very tightly-; on letting go the brachial artery the blood rushes in swiftly, 

 the skin blushes, and the maximal beat quickly returns. 



Many years ago Hurthle(5) noted that the diastolic pressures taken simul- 

 taneously with a manometer at the femoral artery and at the carotid artery 

 were nearly similar, while the systolic pressure at the femoral exceeded that 

 of the carotid by roughly 68 mm. of Hg. Dawson (6) corroborates this state- 

 ment, working with the maximum and minimum manometer, but points out 

 the diastolic pressure in the femoral is always slightly lower than the 

 diastolic in the carotid. 



We would advance the explanation of the higher systolic and lower 

 diastolic readings in terms of the resonance theory. The abdomen 

 functionates as a resonator of the pulse, because each organ in it — liver, 

 spleen, kidney, intestines, etc. — are all pulsating and the cavity is a closed 

 one. Descent of the diaphragm is compensated for by an outward move- 

 ment of the abdominal wall. The abdominal wall is an elastic structure. 

 Consequently the systolic pulse in the aorta and great vessels is surrounded 

 by more or less synchronous pulsations, which, like the well adjusted tap on 

 the moving pendulum, augment its swing. 



In the case of the higher blood-pressure readings in the leg arteries, com- 

 pared to the arm readings found by Hill, Flack, Holtzman and Eowlands (1) in 

 cases of aortic disease, we believe the same resonating effect of the abdominal 

 cavity is at work, together with the better conduction of the pulse wave 

 down the tighter abdominal and leg arteries. 



It was suggested by one of us (L. Hill) in 'Further Advances in 

 Physiology ' (7), that the kidney functionated largely through the mechanism 

 of the arterial pulse. " In the case of the kidney the blood in the capillary 

 network, the tissue lymph, and the urine in the tubules are all at one and 

 the same pressure — the capillary -venous pressure. The whole kidney is 



