118 THE VASCULAR SYSTEM 



Heating to 50 C. also causes a permanent loss of contractility. 

 The carotid behaves to moderate changes of temperature like 

 other unstriped muscle retractor penis of dog, iris and bladder 



FIG. 8. Carotid (ox), contracted. Transverse strip; 8 hours p.m. 

 Second loading after If hours. 



strips of cat, strips of lower portion of gullet contracting on 

 cooling and relaxing on warming. The relaxing effect of warmth 

 is taken advantage of by the surgeon in passing catheters, &c. 



The aorta and pulmonary artery con- 

 tract much less than the carotid, for in 

 them there is less muscle and more elastic 

 tissue. 



In the case of a relaxed artery 

 MacWilliam to whom we owe these 

 observations finds the greatest amount 

 of extension is produced by the first 



FIG. 9. Elongation of con- i T, t -LJ. ct i V.L- 



tracted artery with rise of addition of weight. Successive additions 

 internal pressure, 0-300 mm. cause diminishing increments in length 

 Hg. Length 16 mm. ... , . , , T ?, 



per unit increase of weight. In the 



early part of the process of stretching a contracted artery, the 

 resistance is solely muscular ; later, when the muscular resistance 



