In the first place it will be necessary clearly to comprehend whether there actually exists a spontaneous arteritis, and whether that special form of arteritis ever occurs which is commonly supposed to be met with in our hospitals and dead-houses.

If under the term arteritis we understand an acute inflammation, in which the inflammatory products are deposited or exude, as in phlebitis (inflammation of the serous membranes, &c), on the free surface of the lining membrane of the vessel - that form of inflammation which is supposed to give rise to those appearances of redness commonly observed after death in the inner coat of the arteries - it will be necessary to notice the following points in reference to this subject:

1. The absence of vessels in the (yellow) circular fibrous coat, and more especially in the inner coat of the vessels, forbids our assuming the possibility of inflammation in these layers. This is also fully confirmed by experience, and we find that the redness observed in these coats, more especially in the lining membrane of the vessels, is obviously owing to imbibition, which is developed after death, and possibly even during life, with a rapidity proportional to the state of decomposition of the blood. The coloration always proceeds from the inner surface of the vessel without a trace of vascularity, and penetrates to different depths in the yellow membrane; whilst there is no product of inflammation to be discovered either on the inner surface of the vessel or in the tissue of either of these arterial coats. The phenomena manifested during life by the supposed arteritis, are in such cases always dependent on primary or secondary disease of the blood.

2. The cellular sheath of the vessel is alone capable of inflammation, and we are here led to inquire, whether this inflammation can deposit its products on the inner surface of the artery, under what conditions this may be done, and, what experience teaches us in reference to this subject.

The circular fibrous coat in the larger arteries, as, for instance, in the trunk of the aorta, exhibits so great a thickness, together with such density of texture, that we are unable to comprehend how it can be permeated by an exudation, unless by the agency of an acute process. This is fully confirmed by experience; for, at all events, we have never detected any such process in the trunk of the aorta, or, in other words, never observed arteries in the sense in question; and we are, therefore, led to deny, or at all events to doubt the correctness of the observations recorded in reference to this subject. According to our view, the supposed pseudo-membranes on the inner surface of the aorta, and its redness, together with the fibrinous plug obstructing its canal, are separated and coagulated from the diseased blood.

We, moreover, regard it as very doubtful whether pus is ever produced in the inner coat of the arteries or between this and the middle one, nor do we attach any great weight to the observations of Andral, in which, as he asserts, he found some half dozen abscesses of the size of hazel-nuts under the inner coat of the aorta.

Experience alone is able satisfactorily to determine the limits at which the thickness and density of the texture of the circular fibrous coat cease to oppose an absolute obstacle to the imbibition and permeation of an exudation produced in the cellular sheath of the artery, or to its appearance on the inner surface of the vessel. We find, indeed, from observation, that such inflammation frequently exists in the femoral arteries, especially in women, and likewise in the umbilical arteries of new-born infants; and we are hence led to conclude, that it may occur in all those arteries generally which possess a like organization.

The anatomical appearances of acute arteritis, considered within the limits we have assigned to its occurrence, are:

1. Injection, Redness Of The Cellular Sheath Of The Vessel

This is commonly no longer distinctly apparent after the establishment of those products which we are about to name.

2. Infiltration Of The Cellular Sheath

Infiltration Of The Cellular Sheath, with a serous, sero-fibrinous, partially solidifying moisture, causing puffiness; in some few cases the tissue exhibits purulent exudations, which are either diffused, or limited to individual points, or grouped into circumscribed foci.

3. Extreme Lacerability

Extreme Lacerability - the facility with which the cellular sheath may be removed from the circular fibrous coat.

Hitherto we have only enumerated the appearances attending inflammation of the cellular tissue. (See vol. iii. p. 18).

4. The Circular Fibrous Coat

The Circular Fibrous Coat appears loosened and succulent; admits readily of being drawn into fibres and separated from the elastic coat; is commonly blanched, and sometimes colored in different shades of red from the inner surface of the vessel through imbibition, although without any apparent injection. The lining membrane of the vessel is loosened, and may easily be detached or torn; its free surface is dull, and occasionally exhibits a felt-like or wrinkled appearance; it is either pale or reddened through imbibition.

5. The Vessel

The Vessel is frequently, although not always perceptibly dilated, which is owing to the paralysis of the elastic layer of the cellular sheath and the circular fibrous coat. A coagulum of blood acting as a plug is lodged in the canal of the vessel, whose bore is thus more or less completely filled and obstructed.

6. The Presence Of A Free Product

The Presence Of A Free Product (exudation) covering the inner surface of the vessel in the form of a pseudo-membrane is, in most cases, problematical. It occasionally occurs in the form of a soft, pale yellowish, or yellow-reddish layer, differing from the inner lining membrane of the vessel, as well as from the peripheral stratum of the plug. In more frequent cases, that which may be regarded as a free product, is merely the outer layer of the plug in the act of being metamorphosed into a structure analogous to the inner coat of the vessel. In these cases, the exudation thrown out on the inner surface of the vessel is taken up into the blood before it has been consolidated and has thus given rise to the formation of an obstructing coagulum. In many cases a portion of the exudation is solidified under one of the strata forming the inner coat of the vessel - below the epithelium and the longitudinal fibrous coat - and these strata being thus loosened are thrown off. They form a covering to the plug which projects into the canal of the vessel.

These appearances constitute the so-called adhesive arteritis.