366 



Messrs. L. Hill and M. Flack. Effect of [Mar. 31, 



same tube, (3) through the same tube and same length of tube, but with 

 increasing amplitude. With an entering pressure of 160 mm. systolic and of 

 40 mm. diastolic, a curve taken with the Hurthle manometer from the 

 0'8 mm. tube had all the characters of a " low " pressure sphygmogram — great 

 amplitude, sharp rise and fall and very well-marked dicrotic wave; while 

 with exactly the same entering pressure the curve taken from the - 2 mm. 

 tube took on all the characters of a " high " pressure sphygmogram — slow rise, 

 flat top, slow fall and slightly-marked dicrotism. Using the same tube, it 

 was found that the higher the pressure and the more the " resilience " of the 

 tube was brought into action, the nearer together were the diastolic and systolic 

 pressures at the end of the tube. A length of 30 cm. of 0"2 mm.-thick tube 

 with an entering pressure of 78 mm. Hg diastolic and of 148 mm. Hg systolic 

 gave an almost continuous pressure of 104 mm. diastolic and 107 mm. 

 systolic at its farther end. The same length of 0'8 mm.-thick tube gave a 

 much more discontinuous pressure at its farther end. Lengthening a given 

 tube had a like effect, approximating the diastolic and systolic pressures at its 

 farther end, e.g. by increasing the length of a 0'8 mm. tube from 15 to 30 cm. 

 the difference between systolic and diastolic pressures was diminished from 

 66 to 44 mm. 



. The use of the word "resilience" in the sense given above is not in 

 accordance with the meaning given to this word by the physicist, and 

 in the discussion which followed the reading of the above paper it was 

 suggested by the President of the Eoyal Society that the word " lability " 

 might be suitable. We propose to adopt this word and thus free ourselves 

 from the charge of ascribing to " resilience " an equivocal significance. By 

 the " lability " of an artery, then, we mean the ease with which it distends 

 with a rise and recoils with a fall of pressure. 



We have investigated the effect of the " lability " of arteries on the pressure 

 curve, (1) by means of a simple schema, (2) by interpolating a length of 

 artery between a Hurthle manometer and the carotid artery when recording 

 the blood-pressure curve in the living animal. The schema consists of a 

 piece of rubber pressure tubing, connected at one end to a Hurthle mano- 

 meter and branching into two channels at the other end by means of a 

 T-piece. A short length of rubber pressure tubing forms the channel on one 

 side, and an equal length of artery that on the other side. The two channels 

 are connected by another T-piece to a short length of rubber pressure tubing, 

 which is closed at its farther end. This tube is rhythmically pulsed between 

 the thumb and finger, the whole schema being filled with water to a pressure 

 equal to that of the normal arterial pressure. Clamps are arranged so that, 

 in turn, either the rubber pressure tubing or the artery is made to conduct 



