Plastic phlebitis bears the same relation to suppurative, that the two forms of inflamma tion hold relatively to other organs. Plastic phlebitis indicates a form of disease of milder character, and consummated with results of less severity. Suppurative phlebitis is more or less mixed up with the plastic form, and is generally secondary to it.
When a vein undergoes inflammation, the affected portion throughout its entire thick ness becomes of a diffused red, which is not, at this stage, to be distinguished from the red stain produced by contact of the blood, ob servable, under certain circumstances, in both arteries and veins ; this fades at the edges of the inflamed portion. As the disease advances, the part becomes irregularly mottled of all shades, from purple to the natural colour of the part ; with this appears, in the areolar tissue of the veins, an effusion of sanious serum. The effusion does not end in a serous exudation ; but, as the disease progresses, a plastic effusion is exhibited, not only in the tissue of the vein, but also within its cavity. Whether or not the previously developed serous effusion also escapes in part upon the free surface of the lining membrane of the vein, is not easily de termined, but in the stage now under con sideration it probably does so, as in other serous inflammation. At all events, at or im mediately after the time when such effusion occurs, the tube of the vein becomes blocked up with a coagulum of blood : this does not occur at once, but progressively, beginning by the deposition of fibrine upon the inflamed surface, which deposition is increased by suc cessive layers, the original being for the most part the most compact, until the entire tube is blocked up. That part of this fibrinous product is formed by.the serous lining of the veins,— secreted from the vasa vasorum, —is proved beyond all question by the experiments of Gendrin and Hope. Gendrin found that, by securing a portion of a vein between two liga tures and removing all the blood it contained, upon injecting some irritating substance into it, plastic lymph was exuded in sufficient quantity to fill the cavity of the insulated por tion.* In this experiment the fibrinous matter was clearly true plastic lymph, in all respects similar to the plastic effusion in other serous cavities. Again, the experiments of Dr. Hope, in which, by mechanical irritation, he pro duced warty excrescences on the valve of the aorta, support the view I have taken. There are many points in the formation of these coagula in veins which are remarkable. That they do, as already stated, consist both of lymph-exudation and coagulated blood is more than probable. But what determines the coagu lation of the blood in plastic phlebitis, is less obvious. That the inherent power of coagu lation, which the blood in itself possesses, is the cause, is not saying enough. There are certain conditions which must occur before coagulation can develop itself. While the blood, itself in a state of health, remains in contact with the lining membrane of healthy blood vessels, coagulation is impossible ; but under certain conditions of disease the blood loses its fluidity, and these conditions may either consist in some abnormality of the ves sel's walls, or in some foreign matters becom ing mixed with the blood, —the former in fluence being passive, and the latter an active agent in producing or hastening coagulation.
I would here urge the doctrine that the vascular cavity, —the hollows of all the tubu lar vessels (veins, arteries, and lymphatics), together with the ventricles and auricles of the heart, — constitutes a true serous shut sac, much complicated in form and modified by its peculiar functions, it is true ; but pos sessing the same anatomical elements, — an epithelial pavement placed upon a sheet of limitary tissue, on the other side of which is situated a nutrient vascular system. 1 would here urge this view, because it applies with much force to certain questions in venous pathology, and to few more so than the one under consideration, where arguments by analogy are a desideratum. The lining mem brane of the veins then is a serous membrane. On the surface of other serous membranes pleura, pericardium, &c. —plastic effusion con sists of sheets of lymph, and a certain amount of serum. By analogy we, et priori, conclude that lymph is effused in inflammation on the lining surface of the veins, and this the experi ments of Gendrin and Hope have established by indisputable proof. That the inflammatory product consists partly of serum as well as lymph is supported by analogy alone ; but if admitted would explain the coagulation of the blood to complete the clot, which is known to be so much facilitated by the ad mixture of foreign or abnormal secretions. Whatever may be the opinion of the forma tion of the coagulum, its characters are these : —it consists of concentric lamina?, brownish, yellowish, or white, of which the central are the darkest and softest; and sometimes the centre is nearly fluid blood. The density of the entire clot is subject to much variety. The coagulum is moulded to the cavity of the vein, and sometimes present the exact impression of the valves. Mr. Arnott has made an interesting observation with respect to the coagulum, that it extends along the affected vein usu ally to the next collateral branch, and there abruptly ceases. The true explanation of this circumstance is doubtless that given by Mr. Henry Lee.* " When any portion of a vein is obstructed, the blood is kept at rest between the obstruction and the next collateral branch ; and, if disposed to coagu late, there is nothing to interfere with such an action. But the case is different as soon as one vein opens into another. A fresh cur rent of blood is then continually sweeping the orifice of the obstructed vessel; and even although the blood at this point should have a tendency to coagulate, it is carried on in the course of the circulation, before it can adhere to the sides of the unobstructed vein." The coagulum thus extends towards the heart, beyond the limits of the inflamed por tion, having a mere mechanical boundary. it extends also at the distal end, but here it becomes gradually attenuated : it often rami fies into many branches and subuivisions of the veins that are tributary to the one ob structed, especially where they are not re lieved by collateral anastomoses. At those points where inflammation has not occurred, and the coagulation has been favoured by me chanical circumstances simply, the clot scarcely adheres to the lining membrane of the vein.