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



pressure of 80 mm. of Hg before the pulse again disappears. We find 

 the systolic blood-pressure readings rise successively from 70 mm. to 

 80-90-100-110-120-130-140 mm. of Hg. There may, or may not, be a 

 rebound effect when the blood pressure rises, for a short period, above 

 what it was at the commencement of the experiment, and above the reading 

 in the forearm of the other arm. 



The ischemic limb on the abolition of pressure in the armlet on the upper 

 arm is found to gradually swell and becomes red. There is obviously a 

 marked vaso-dilatation. 



Bayliss (4) has shown that when the blood pressure is taken off a limb or an 

 organ, e.g. by blocking the abdominal aorta, an increase in volume of the 

 limb or organ occurs when the block of the aorta is removed. Bayliss offers 

 no proof as to which part of the vascular mechanism dilates in this reaction. 

 A study of the phenomenon in a limb with an aberrant radial artery during 

 this experiment gives a clue to the vascular conditions present in the reaction. 

 The aberrant radial artery can be seen to dilate. It stands out like a small 

 worm on the back of the wrist. The veins on the forearm also dilate. It is 

 unlikely that the arterioles are constricted when there is visible an increased 

 blush of the capillary area. We conclude that during Bayliss' phenomenon, 

 after a bandage has been used to make the limb ischeemic, the main arteries 

 as well as the arterioles of the limb dilate. 



This can be proved by tracings taken with the Dudgeon sphygmograph 

 from the aberrant radial artery on position L We use weight extension to 

 fix the Dudgeon. The base line of the tracings is seen to progressively rise 

 as the artery dilates. Care must be taken to fix the limb effectively during 

 this experiment. 



A further proof that the main arteries are dilated can be got by plunging 

 the congested limb into ice-cold water. After a period in the cold water the 

 artery is felt to be very much constricted, and this is confirmed by visual 

 examination. Massage of the artery brings it back to its original dilated 

 condition. 



A modification of this experiment, viz. releasing the artery and taking the 

 blood pressure in the ischaemic limb as the limb fills with blood, can be 

 performed. The ischsemic limb with an armlet on the upper arm at a 

 pressure well above the ascertained systolic blood pressure can be plunged 

 into ice-cold water with ice in it. After a short period the limb, withdrawn 

 from the ice-cold water, is found to be thoroughly chilled and is dried by 

 mopping lightly without rubbing. Subbing might dilate the arteries. When 

 the pressure is let down suddenly in the armlet, at first the pulse can be 

 damped down by 40 to 50 mm. of Hg, then the pressure rises, but much more 



