186 THE MOTION OF THE BLOOD. 



failed in the application of electricity to parts indisputably 

 muscular; Verschuir g in the case of the heart and urinary 

 bladder, and Zimmerman in other parts of known muscularity. h 

 Dr. Hastings caused contraction in veins also by the application 

 of stimuli. i 



Dr. Parry instituted a number of experiments upon this ques- 

 tion. After exactly ascertaining the circumference of arteries in 

 animals, he killed them, and again measured the circumference ; 

 and after a lapse of many hours, when life must have been per- 

 fectly extinguished, he measured the circumference a third time. 

 Immediately after death, the circumference was found greatly 

 diminished, and on the third examination it had increased again. 

 The first contraction arose from the absence of the blood, which 

 distended the vessels and antagonised its efforts to contract ; and 

 it was evidently muscular, or, to speak more correctly, organic, 

 contraction, because, when vitality had ceased, and this kind of 

 contraction could no longer exist, the vessel was, on the third 

 examination, always found enlarged. k 



The forced state of distension in arteries was proved by the 

 contraction immediately occurring on making a puncture in a 

 portion of vessel included between two ligatures. An experiment 

 of Magendie's is of equal weight, in which a ligature was fixed on 

 the whole of a dog's leg except the crural artery and vein, and 

 the vein and artery were compressed, when, upon wounding the 

 vein, the artery completely emptied itself. l The capacities of 

 arteries are thus always accommodated to the quantity of blood, 

 and this circumstance gives the arterial canal such properties of 

 a rigid tube as enable an impulse at the mouth of the aorta to be 

 instantly communicated throughout the canal. This appears the 

 great office of the contractile powers of arteries, for, 



e 1. c. expt. 22. h De irritabilitate. l 1. c. p. 52. sq. 



Dr. M. Hall thought he found an artery, which branches off from the vessels that 

 by their union form the aorta in the frog and toad, pulsate a considerable time after 

 the removal of the heart, becoming straight and pale; whereas the pulmonary artery 

 grows more tortuous and distended at the moment of the stroke of the heart. 

 This, however, is no more a proof that arteries in other animals have muscular 

 powers, than it is that other arteries in the same animal have muscular powers 

 and exhibit the same phenomenon: and Dr. Miiller (Ph, Tr. 1833) maintains 

 that the vessel is a vein which beats only from the impulse of lymph sent into it 

 through a lymphatic by a lymph-heart. 



k See also J. Hunter, On the Blood, pp. 114. 116. 



1 Journal de Physiologic, t. i. p. 111. 



