The Cellular Sheath Of The Vessel, in the majority of cases, is found to be in a state of chronic inflammation - that is to say, in a state of vascularity, redness, infiltration, and puffiness, or has been converted, in consequence of this process, into a layer of white, very dense, callous tissue of considerable thickness, coalescing with the circular fibrous coat, or with the deposit within its interstices. The following points are of the greatest importance in reference to this condition of the cellular sheath: a. The intensity of this condition bears no relation whatever to the degree of the deposition, since, in the higher stages of this process, it is occasionally, and in the less developed stages very frequently absent, whilst it never exists in the incipient form of the deposit.

b. This condition must, therefore, be of a secondary character, and associated with a certain stage of the deposit. This fact does not, however, exclude the possibility of the converse relation, for as we shall have occasion to show, a primary and substantive chronic inflammation of the arterial sheath may give rise to a local deposit, in consequence of dilatation of the vessel.

The deposit is either local, limited to one or more spots of the vessel, or it extends over a large portion of an artery, or over a separate part or the whole of the arterial system. In the former case it depends on local dilatations of the vessel, and on the slowness or partial stagnation of the current of the blood; in the latter, the controlling influence must be a general state of disease, which we would designate as a constitutional condition.

The deposit, when appearing as a constitutional disease, occurs almost exclusively in the arteries, and only in the aortic system. This agrees with the consecutive anomalies, especially the occurrence of ossification of the vessels, aneurismal formation, and obliteration.

Very little relative importance can be attached to any scales purporting to give the frequency of the occurrence of this constitutional affection in the different portions of the aortic system, for whenever the disease appears especially developed in any definite part, the rest of the system - as, for instance, the aortic trunk - will also be implicated.

The trunk of the aorta is most frequently the seat of the disease; and here we find that the ascending aorta, and the arch, are most commonly affected, next the abdominal, and lastly the thoracic portion.

Next in order follow the splenic, the femoral, the internal iliac, the coronary arteries of the heart, the trunks of the arteries of the brain - that is to say, the carotids within the cranium and the vertebral arteries, with their branches, - the uterine, the brachial and subclavian, the spermatic, the common carotid, and the hypogastric arteries.

It is worthy of notice, that certain arteries are only very rarely, and in exceptional cases, subject to even a subordinate degree of this disease; among these we may reckon the mesenteric arteries, and yet more, the coeliac, the gastric, the hepatic, and the epiploic.

This scale corresponds generally to the frequency of the occurrence of metamorphoses in the deposit, such as its ossification, as well as aneurismal formations.

We have not been able to determine, with the requisite accuracy, whether there actually exists such a symmetrical occurrence of the conditions already described (viz.: crude deposition, ossification, and the atheromatous process) in the corresponding arteries of the two sides of the body, as Bizot maintains that he has observed, and regarding which he has established a law; and indeed our views of the constitutional character of the disease prevent our attaching any great importance to the subject.

This disease is of very rare occurrence in the pulmonary artery and its branches; but if it be present here, it is always likewise considerably developed in the aortic sytem.

This affection scarcely ever occurs as a constitutional one in the veins, for here it always exists as a secondary phenomenon, depending on a sluggishness of the current of the blood, produced by ordinary causes. (See Diseases of the Veins.) On the other hand, the veins are frequently affected by a morbid formation, which, although it may not be purely constitutional, yet presents a very remarkable analogy with the disease of the arteries under consideration: we refer to the so-called phlebolites or vein-stones. It is, moreover, worthy of special notice, that the deposit in the veins commonly attains a high degree of development when arterial blood makes its way into them. (Varicose Aneurism).

Sex exercises no special influence on the occurrence of the deposit and its different consecutive conditions; but Hasse appears, on the whole, to be correct in his view, when he states that disease of the abdominal aorta is more frequent, and more highly developed, in women than in men.

Age, on the other hand, gives rise to important differences; but although the disease is most frequent between the fortieth and the sixtieth year, the assertion that it increases in frequency in proportion to the age, and that it occurs in advanced life almost as a normal condition, is not well grounded; for although it may undoubtedly date in many aged persons from a comparatively early period of life, there are many others in whom it is entirely absent. Old age presents, indeed, a mechanical disposition to this affection, from the dilatation of the arteries common to that period. Before the above-mentioned age, the disease is undoubtedly more rare, although frequent even between the thirtieth and fortieth year. Before that period it is very much rarer; and when it occurs prior to the age of twenty years, it is mostly only a local disease, depending on congenital or early acquired anomalies of the trunks of the vessels and of the heart. This observation refers especially to its occurrence during the periods of puberty and childhood.

If, after considering the above remarks, we proceed to the question - In what consists the nature of the disease? we gather the following facts from our examination of all the important points bearing on the subject:

1. The deposit cannot be regarded as the product (exudation) of an inflammation of the arteries. The chronic inflammation of the cellular sheath of the diseased vessel is almost always a secondary consecutive appearance which associates itself with the already established deposit.

2. The deposit is an endogenous product derived from the blood, and for the most part from the fibrin of the arterial blood.

3. Its formation demonstrates the pre-existence of a peculiar crasis of the blood, which is intrinsically arterial, although at the present time we are wholly ignorant of the character of the peculiarity on which this depends. We must regard the old dogmatic view, which sought the cause of the affection in arthritis, as an opinion deficient in proof.

4. In proportion to the extent of the disease of the arteries, so much the less likely is it to be combined with tuberculosis; and this disease undoubtedly is in part the cause of that immunity against tuberculosis which we constantly notice in large aneurisms of the trunk of the aorta. The grounds of this relation are not known; but it is not wholly improbable that this immunity may arise from a similarity between the process of deposition (which occurs in the form of separation of fibrin), and the tuberculous process, by exhausting the arterial character and the materials of the blood. On the other hand, we very frequently observe an excessive production of fat associated with the deposition and ossification in the arteries. This abnormal formation occurs - independently of the fatty degeneration of the circular fibrous coat, and of the atheromatous process, - more especially in the neighborhood of the ossified arteries with atrophy of the muscular tissue, in the vicinity of aneurisms, and, in addition, as excessive accumulations of fat in the blood, of cholesterin in gall-stones, etc.

5. The deposit and its metamorphoses present numerous, highly important analogies, that have hitherto been wholly neglected. For the sake of brevity we will here notice only the most important; viz.: the deposit also occurring under certain conditions in the veins, the phleboliths (which we will consider under Diseases of the Veins), the capsules investing different fibrinous coagula in the vascular system, and causing them to adhere to the walls of the vessels and of the heart, and the metamorphosis which these fibrinous coagula undergo within the vascular system, and which may even affect fibrinous coagula externally to that system.

The effects produced by this disease in its reaction on the whole organism are still unknown. In respect to the vessel itself, the disease gives rise to different forms of dilatation, with contraction of its branches and complete closure of their mouths, constituting a highly important, although little known, secondary condition. When arteries of lesser calibre have been ossified, and the deposit continues to exist, they finally become closed and obliterated. It is, moreover, probable that the capillary arteries at the seat of the deposit become diseased, in consequence of the diminution and cessation of nutrition arising from the obstruction and arrest of their permeability. Either may, moreover, give origin to the formation of spontaneous gangrene - the so-called dry gangrene - mummification of the tissues. Finally, this disease is often found to terminate in spontaneous laceration of the large arteries, and especially of the small trunks.

It still remains for us to add the following remarks to the observations already made in reference to the diseases of the valves of the heart at p. 174. The valves of the aorta exhibit a thickening and an adhesion to the wall of the vessel, and appear fused together with consecutive shrivelling, malformation, and ossification. We have already remarked, in the same page, that this disease which generally forms the basis of that insufficiency of the aortic valves which is slowly and almost imperceptibly developed in advanced life, is not of endocarditic origin, but depends upon an excessive formation of a tissue analogous to the inner coat of the vessel, and deposited from the blood upon these valves. It is commonly associated with a diffused deposition in the trunk of the aorta and a dilatation of the latter with aneurismal formation.