1901.] Properties of the Arterial and Venous Walls. 



147 



20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 



Fig. 30. — Same artery as in fig. 29 ; second elevation of pressure 24 hours after 

 the first. The extensibility is seen to be much increased, though the general 

 behaviour in giving enlarging increments of volume per unit rise of pressure 

 is not changed. 



In other cases where the artery is only slightly contracted, and the 

 maximum distensibility is found at, say, 100 — 120 mm., a second rise of 

 pressure causes the maximum distension at a much lower level — e.g., 

 a t 40 — 60 mm., or, it may be, immediately above zero. (Compare 

 figs. 28 and 31.) 



20 40 60 80 100 120 140 160 



Fig. 81. — Second elevation of pressure in same portion of artery as in fig. 28, half 

 an hour after completion of first experiment. 



Such effects of repetition of the rise of internal pressure are mani- 

 fested whether the second rise is induced very shortly after the first 

 one (a few minutes) or after an interval of 24 hours or more. In the 

 latter case the change may be more extensive than in the former — 

 owing no doubt to the lapse of time leading to a diminution of the 

 contraction present in the artery. 



As regards the recovery of a contracted artery after it has been 

 distended by internal pressure, this is often quite complete — at least 

 when the artery is tested at a relatively early stage of post-mortem 

 contraction, e.g., within a day or two after death. The oil which has 

 been driven out along the horizontal graduated tube when the artery 

 expands under the increase of internal pressure returns quite to the 

 starting-point ; indeed it often moves back beyond its starting-point — 

 showing that the artery has not only completely recovered from dis 

 tension, but has contracted somewhat in volume from what it was at 

 the beginning of the experiment. 



