It has been shown upon very high authority, that the sides of a vein do not unite after venesection (as has sometimes been presumed to be Mr. Hunter's opinion); but that the divided edges only of the vessel are agglutinated by the coagulum, which "serves as a bed to the new membrane." But the case is different, should this first attempt at union fail; the sides of the vessel may then become united, and its cavity for a time obstructed (section IV). The approximation of the sides of the veins would materially facilitate this action, which is the natural security, under the circumstances, against the admission of foreign matter. When an abscess is suspected to have formed in a vein, a similar mode of treatment is recommended by Hunter; the compress, in this case, being placed between the inflamed part and the centre of the circulation. In the pathological museum of the College of Surgeons, one of Mr. Hunter's preparations (No. 1728) exhibits such a case, where, from the imperfect union of a vein, the contents of the abscess had become mixed with the blood. As the process of reparation has been variously described by authors, so the different theories propounded have led to different kinds of treatment. At the Veterinary College, even within the last few years, it was publicly taught, that a coagulum in a vein was a foreign substance, and ought to be removed; and the jugular vein in horses which had been bled, was sometimes slit up for several inches, in order to remove the coagula which formed in successive portions of its course. That a coagulum in a vein may be an irritating substance has been fully proved (sections I and II); but the irritation depends upon the accidental admixture of foreign matter: and the inflammation of the veins, produced by the contact of impure blood, requires to be carefully distinguished from the natural mode of union by the first intention.