1901.] Properties of the Arterial and Venous Walls. 151 



The artery was usually first tested in its contracted state, then 

 relaxed by one or other of the methods mentioned, without any dis- 

 turbance of the cannula or plug, and again tested in the same way as. 

 before. (Compare figs. 32 and 34.) 



Fig. 34. — Artery, relaxed by keeping in warm chamber at 39° C. for 24 hours. 

 Same portion of artery as was usod (in contracted state) in fig. 32. 



The relatively great tendency to elongation, even under low or 

 moderate internal pressures, in a relaxed artery is important with 

 regard to the tendency of certain arteries in the human body to become 

 elongated and tortuous, apart from any recognisable structural change 

 in the vascular wall. Elongation of the healthy temporal artery when 

 relaxed is easily discernible even in young subjects ; prolonged and 

 frequently-recurring periods of relaxation tend to induce a more or less 

 distinctly tortuous condition. Prolonged relaxation of the arteries of 

 the uterus and mamma during pregnancy leads to similar changes 

 in them. 



Pulsatile Expansion of Relaxed and Contracted Arteries. — I have ex- 

 amined the pulsatile expansion of arteries when a rhythmical series of 

 elevations and depressions of internal pressure is mechanically pro- 

 duced — in imitation of the rhythmical changes of pressure caused in a 

 normal artery by the pumping action of the heart. This was tried 

 when the pressure within the artery was at zero to begin with, or 

 when a certain height of pressure had first been established; the 

 apparatus for testing distensibility already described was used. Khyth- 

 mical compression of a rubber tube containing air in connection with, 

 that filling the interior of the artery was used to produce the pulsatile 

 variation of pressure. The changes in the volume of the artery in 

 response to the variations of pressure in its interior were shown by 

 the to and fro movement of the oil in the horizontal graduated tube. 



