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



beat is slower in the ischsemic limb than in the congested limb, that we 

 have herein a natural explanation of the initial low pressure readings. 

 The pulse beats in the ischeemie limb are of feeble force, consequently the bag 

 of the sphygmometer applied to the artery naturally damps down the feeble 

 beats. But we have shown that maximal beats, whether the artery is 

 dilated or contracted, suffer a damping-down in the aberrant radial artery 

 at extremely low blood pressures. Thus in one experiment, when the 

 systolic blood pressure was taken at heart level by Hill's sphygmometer in 

 the forearm at position III and was found to be 120-130 mm. of Hg, the 

 returning pulse in the ischaemic limb at position III was damped down at 

 70 mm., and when the blood pressure rose at position III to 120-130 mm. 

 the pulse in the aberrant radial artery at the back of the wrist at posi- 

 tion I where maximal beats could be recorded was damped down at 

 50-60 mm. The feebler pulse beats in the forearm on the radial artery 

 at position III required 70-80 mm. to damp them down. The maximal 

 beats on the same radial artery at position I required only 50-60 mm. of 

 Hg to damp them down. We see, in fact, that the pulse beat, no matter 

 how forcible, can be damped down by a pressure 70 mm. of Hg or so below 

 normal blood pressure. 



It might be argued that the low blood-pressure readings obtained in this 

 experiment represent the actual blood pressure in the radial artery, that 

 there has been a fall of head of pressure as the blood flows into the ischaemic 

 limb. It is not probable that the head of blood pressure would fall greatly, 

 because the blood flows through the narrow arterioles and still narrower 

 capillary bed. ISTo matter whether the arterioles and capillary bed are full 

 or empty, the resistance to the blood stream remains in the friction of the 

 vessel walls. But blocking the radial artery below the point of measurement 

 effectively removes the objection that there is a fall of head of pressure. 

 It might be argued that the fall of pressure continues down the ulnar artery. 

 But by blocking the radial artery one converts the radial artery into a side 

 tube measuring lateral pressure from the brachial at the elbow, and the 

 lateral pressure of the brachial artery at the elbow would not fall. Further, 

 one can block both radial and ulnar arteries, and the pressure readings taken 

 from the forearm of the ischaunic limb show the same progressive rise. "We 

 conclude that on suddenly lowering the pressure in the armlet the blood 

 pressure rapidly becomes normal, and the low blood-pressure readings, as 

 measured by the disappearance of the pulse, are false, both in the ischaemic 

 limb and in the cold ischaemic limb. 



The explanation of these low blood-pressure readings lies in the diminished 

 resonance of the empty tissues. The mass of tissue below the bag is not 



