666 CIRCULATION. 



of the arteries as of a muscular nature, was un- small ligature had been half tightened around 

 successful in producing obvious contractions in it." So also in Experiment 24th, he relates 

 them. The repetition of the experiments of that a part of the carotid artery of a ewe was 

 Verschuir by many others has been attended diminished by a third of its original diameter 

 with very various results ; some confirming his under exposure, after having been half an hour 

 observations, others having entirely failed in denuded, while the neighbouring parts had be- 

 producing any obvious contraction, or not being come rather dilated, and that while he was pro- 

 disposed to consider it of a muscular kind, ceeding to measure one of these dilated por- 

 Among the last may be mentioned Nysten, tions, he " saw it shrink to nearly the same 

 Bichat, Wedemeyer, and J. Miiller. size as the constricted part." It appears to us 



It must be obvious that, laying aside the manifest, that, whether these irregular diminu- 



difference of opinion regarding the nature of tions of the diameter of the artery, obviously 



the contractions when they are admitted to occasioned by a shortening of its fibres, are at- 



occur, in a question of this kind a positive re- tributed to the exposure of the artery to the air, 



suit deserves more consideration than a nega- or the violence done during the dissection of it 



live one, provided the phenomena stated to by the scalpel, they must equally be regarded 



have been observed are such as to be appre- as the consequence of stimulation of one kind 



ciable by all. Among the experiments favour- or other, and are therefore of the nature of mus- 



able to the view that the large arteries are en- cular contractions. 



dowed with irritability, may be mentioned those Hoffmann first noticed the contractions of 



described by Hastings,* and a series of unpub- the arteries from the application of acrid che- 



lished observations by Dr. Thomson, to which mical stimuli to their coats ; and it appears 



we have access, which seem to prove in a very from numerous subsequent experiments, that 



satisfactory manner the frequent occurrence of contractions are more readily induced in this 



-contractions in the larger arteries after stimula- than in any other way. Were there no other 



lion ; and to point out as a cause of the failure proofs of the contractility of the arteries than 



of some at least of the previous experiments, those derived from the effect of chemical 



the long time which commonly elapses between agents, we should not feel inclined to place 



the application of the stimulus and the occur- much reliance on them, on account of the pos- 



rence of the contraction ; together with the cir- sibility of there having been induced a perma- 



eumstances formerly remarked by Verschuir, nent alteration of the texture from chemical 



that the contraction is not an invariable conse- action ; but the results of such experiments 



quence of the stimulation, and that it occurs form an important confirmation of those which 



much more readily in some animals than in are performed with mechanical and galvanic 



others. irritation. We cannot, however, acquiesce in 



According to Dr. Thomson the contraction the opinion of Wedemeyer* and others who 

 of the larger arteries is in general not percepti- compare the distinct and well-marked contrac- 

 ble before from three to ten minutes after the tions of particular parts of the arterial tubes, 

 application of the stimulus. When galvanism such as those above alluded to, to the general 

 is used, the shocks need not be strong, but constriction of other textures, and more parti- 

 must be frequently repeated in order to induce cularly to the shrinking of the skin which 

 contraction. occurs from the influence of cold, passions of 



Many have remarked the gradual or sudden the mind, &c. 



contraction of the trunks of arteries which have From these considerations we are induced to 

 been laid bare in Man as well as in the lower adopt the opinion that the contractions which 

 animals. When exposed, an artery is some- under certain circumstances occur in the ar- 

 times equally contracted for some length along teries resemble muscular contractions more 

 its tube ; at other times its surface assumes a nearly than any other vital phenomenon. The 

 waved appearance from the occurrence of irre- positive evidence of direct experiment obviously 

 gular contractions or alternate contractions and proves that the contractions in general follow 

 dilatations, and not unfrequently the coat of the application of some stimulus to the artery ; 

 the artery is much constricted at one point but these contractions differ from that of mus- 

 only, as if a tight cord had been passed round cular parts chiefly in the length of time which 

 it. Appearances of this kind, which seem to elapses after the application of the stimulus 

 indicate very distinctly the possession of the before the change of size begins, in the slow- 

 property of irritability by the arteries, are well neS s with which the contraction is succeeded 

 known to many surgeons ; they were noted by by relaxation, and in the want of obvious cor- 

 Drs. Jones and Thomson, in the experiments respondence between the force of the stimulus 

 upon which Dr. Jones's work on Hemorrhage and the extent of contractions which follow it. 

 was founded ; and also by Dr. Parry, who Besides the more marked contractions of 

 nevertheless refuses to consider them as irri- parts of their tubes, the arteries are subject in 

 table contractions. At p. 74 of his work various circumstances to undergo a slow and 

 on the Powers of the Arteries, Dr. Parry, gradual diminution of their diameter through- 

 referring to Experiment 13th, says, "thus a out their whole length, which is considered by 

 very narrow ring of the carotid became, while many physiologists to indicate the possession 

 it was under examination, contracted as if a by them of a property of the nature of contrac- 



* Inang. Disserrat. Edin. 1817, et loc. cit. See tillt y dlflferent from irritability in its pheno- 

 also Hunter on the Muscularity of the Arteries, 

 Jidiu. Meu. arid Surg. Journ. xxii. \). 256. r Loc. cir. 



