116 VASCULAR SYSTEM. 



Q. On what structures do these two kinds of. extensi- 

 bility depend? 



ft. That of the diameter depends on the circular fibres 

 of the peculiar membranes; the longitudinal on the exten- 

 sibility of the common lining membrane and its folds, for 

 there are no longitudinal fibres in either coat. 



Q. What results from the limited extensibility of the 

 peculiar or fibrous coat of the arteries? 



ft. Its rupture in aneurism. The more slowly the dis- 

 tention of the peculiar coat is made, the greater the extent 

 to which it may be carried. 



Q. How is arterial contractility to be divided? 



ft. Lake extensibility, it is transverse and longitudinal. 



Q. Give instances of transverse, arterial contractility. 



A. The union and closure of the umbilical artery and 

 ductus arteriosus; the emptying of an artery between two 

 ligatures; the closure of a tied artery from the ligature up 

 to the first branch given off; and the diminution of the 

 calibre of arteries in profuse haemorrhage. 



Q. How do you account for a small and large pulse? 



ft. The contraction of the artery when empty consti- 

 tutes the small pulse, and the expansion when full of blood 

 the large one. 



Q. Are contractility and irritability the same? 



ft. They are entirely different; for contractility is a 

 property of texture, irritability is a vital property. Con- 

 tractility continues for a long time after death, irritability 

 soon disappears; contractility results from the absence of 

 extension, irritability is the result of stimulus applied. 



Q. What important consideration do you infer from 

 this distinction? 



ft. The superiority of that system should be well re- 



