150 



violent extension of the ham. In looking over the cases that have been 

 recorded, it will be seen, that a considerable number of aneurisms of the 

 aorta, have been occasioned by too forcible arid too sudden an extension of 

 the trunk in raising a heavy burthen. 



From the dryness, the frailly of the yellow or fibrous coat of arteries, 

 the application of ligatures to these vessels is attended with a speedy la- 

 ceration of their tissue; a moderate degree of compression is sufficient 

 to rupture that coat, the external and internal remaining, at the same 

 time, uninjured, provided the constriction be not excessive. Why is the 

 arterial tissue, almost the only one on which ligatures require to be ap- 

 plied, the least fitted of all the organic tissues to bear them ? This incon- 

 venience attending the ligature of arteries, led Pouteau to prefer tying 

 arteries so as to include the surrounding soft parts within the ligature, 

 though this process is, in other respects, less eligible. The objections 

 will be obviated, by employing flat ligatures, which, by acting on a great- 

 er surface of the artery, are less likely to divide the coats of the vessel, 

 which will become obliterated at the spot to which the ligature is applied, 

 the more rapidly as the patient is younger and stronger. 



I once saw, in a man whose thigh was amputated, on account of caries 

 of the knee joint combined with a scorbutic affection, hemorrhage attend 

 the fall of the ligatures, which did not come away till nineteen days after 

 the operation; as if the fibrous coat of these arteries, partaking in the 

 debility of the muscular organs, had not preserved a sufficient degree of 

 contractile power to close the cavity of the vessel. 



LVJI. The contractile power of the arteries is in their middle coat, 

 it is greater, as this coat is thicker in proportion to the calibre of the ar- 

 tery. Hence, as Hunter observes, in his work on the blood and inflam- 

 mation, the larger arteries are endowed with elasticity, merely, while 

 on the other hand, contractility is very apparent in those of a smaller ca- 

 libre, and is found complete in the capillary vessels * ; hence, in the trunks 

 near the heart, the progression of the blood is effected, chiefly by the 

 impulse which it receives from the heart, and as Lazarus Riviere ob- 

 served, the circulation of the blood in the large vessels, is more an hy- 

 draulic than a v tal phenomenon. The action of the main arterial trunks, 

 near the heart, has so little influence on the motion of the blood sent in- 

 to them by that organ, that the aorta is frequently ossified, without af- 

 fecting the circulation. The aorta is n&urally bony in the sturgeon. J. 

 L. Petit, in the case of a bookseller, whose leg he had taken off, found all 

 the arteries of a certain calibre in a state of ossification; they were indu- 

 rated, and of course, incapable of acting, in the slightest degree, on the 

 column of blood which flowed along them. All these facts seem conclu- 

 sive arguments in favour of those physiologists, who explain, on theprin- 



* This is not altogether correct. Every portion of the arterial system is unquesti- 

 onably possessed of the property of contractility. In the larger vessels, muscular fibres 

 are even demonstrated to the eye. Besides, mere elasticity will not explain many of 

 the phenomena of arterial action. Contrary to the doctrine of Mr. Hunter, it was mam- 

 tained by Baron Haller, and indeed by almost all the coteroporary physiologists, that 

 contractility belongs exclusively to the large and middle sized arteries. In this, how- 

 ever, they were deceived. 



It is now well ascertained, that muscularity increases exactly as the vessel recedes 

 from the heart, the capillaries having it in the greatest degree. As far as I know, this 

 opinion was originally taught by Cullen, and afterwards fully confirmed by the experi- 

 ments of Hunter. Chapman. 



