Vascularity, in truth, belongs as little to the nature of tubercle as organization itself. Still it is undeniable that bloodvessels are sometimes met with in tubercles. Two cases are here possible. In the first case bloodvessels may appertain to textures which, whether normal or pathological, - membranaceous areolar tissue, for instance, - had become involved in the tubercle when first thrown out. One or more bloodvessels may traverse the tubercle, previous to an injecting mass, - others impermeable.

In the other case the bloodvessels penetrating the tubercle are doubtless new-formed vessels, and have sprung from an organizable blastema, effused together with the tubercle and incorporated in it. This is attested more especially upon serous membranes, where, as a consequence of inflammation, tubercle becomes deposited along with a considerable portion of blastema, the rudiment of vascularized new textures.

To sum up: the purer the tubercle, the more certain is its estrangement from all bloodvessel formation. The less pure, that is, the more organizable blastema it has incorporated, or consociated with, the more susceptible is it of bloodvessel formation.

We have hitherto spoken of tubercle as being an exudate, - a secretion from the vascular system; of which we hardly deem it requisite to furnish proofs. Here, however, a double question suggests itself, namely, first, concerning the seat of tubercle; and, secondly, concerning a very weighty point, namely, the local process of tubercle production.

The seat of tubercle, as exudate, is at any point of any texture, extraneous to the bloodvessels. Wherever there is a capillary range, a deposition of tubercle is possible. The seat of tubercle is without doubt precisely, or at least in close proximity to, the spot of its exudation, its blastema being in the highest degree coagulable. It is most probably for this reason that it does not affect textures nourished from a distance by a slow imbibition of their substance with plasma, - for example, cartilage. We can ourselves testify to the occurrence, both in larger bloodvessels and in the capillaries (as depots or metastases), of coagula obviously of a tuberculous nature. These are, however, only exceptional cases, and the doctrine propounded in accordance with them is founded rather upon the results of so-called tubercle created by artificial injection. It is evident, however, that the tubercle-like depots so formed were due either to infection of the blood, or to the obstruction of bloodvessels, and that no inference can be drawn from them as to the spontaneous formation of tubercle.

Assuming, therefore, tubercle to be an exudate - an effusion out of the vascular system - the question as to the topical process would resolve itself into this: what are the processes in whose sequel tubercle is thrown off from the circulation? To this we can only reply, that tubercle, like other blastemata, exudes, now almost insensibly in the act of nutrition; then, again, in the sequel to obvious (active) hyperaemia; and lastly, as a consequence of still more manifest inflammation.

1. It is a fact that the incipient production of tubercle takes place, within some organ, - most commonly the lung, and at one particular portion of it, the point de depart, so to term it, of tuberculosis, - in a manner almost imperceptible both to the patient and to the looker-on. The after-death examination reveals no inflammation, or such only as may with far greater probability be interpreted as consecutive. The tubercle is for the most part the gray, withering, and only now and then the yellow, softening, cretefying tubercle.

2. In other cases, on the contrary, a marked hyperaemia of the implicated organs manifests itself during life, and is discoverable after deatb, as the source of the tuberculous exudation. The tubercle is deposited numerously, and also rapidly.

(a.) This tubercle has commonly the form of those scattered granulations, of about the size of millet-seeds, and seldom that of yellow hemp-seed- or pea-sized nodules.

(b.) Its blastema is commonly that of the gray tubercle, often combined with that of the yellow; rarely the yellow alone.

(c.) Not only is it thrown out rapidly and in great numbers, either all at once, or in successive outbreaks repeated at short intervals; but it scarcely ever restricts itself to a single organ, and whilst seemingly perhaps concentrating its main forces upon some one organ, it assails several others simultaneously, often leaving hardly any of the soft paren-chymata unscathed. The tubercles are marked by their uniform size and character, and by the equable distribution with which they are scattered throughout the textures. After their repeated and copious exudation, they gradually become less firm, softer, glutinous, until the fibrinous tubercle - the fibrin being expended - changes into the albuminous tubercle.

(d.) The effusion of the tubercle as a coagulable blastema is always associated with that of a non-coagulable or less coagulable, serous, sero-albuminous, jelly-like, adhesive product, - as a sort of vehicle for the first. The textures are manifestly congested; and, around the tubercles, more or less uniformly infiltrated with the product just referred to.

(e.) The more generally and more rapidly the tubercle-production extends through the organism, the greater the multitude of tubercles, the more marked those dyscrasial appearances wrought by defibrination of the blood, - by so much the more fully does the general disease partake of the acute character. As the expression of that defibrination, the blood appears thin and watery, the attenuated blood-serum, tinged with appropriated haematin, being thrown out upon and coloring the imbibed textures, which, if highly vascular, appear lax, flabby, and drenched.

(f.) As this tuberculosis for the most part proves quickly fatal, a metamorphosis of the tubercle is proportionately seldom observable.

(g.) Rare instances excepted, this tubercle is not the primitive one. Tubercle has commonly pre-existed, whether in an advanced state, or retrograding to decadence, in some organ or other; for instance, the lungs or the lymphatic glands.

3. In fine, tubercle is frequently thrown out in the sequel of inflammation. It is the product of such inflammation, and its sole distinguishing feature. These inflammations occur in every part, but more particularly upon mucous membranes, and in the larger serous sacs, where they may be most advantageously studied. Thus they are seen especially upon the peritoneum and pericardium, and again upon the mucous membrane of the uterus, of the tubae, and of other ducts, as the vas deferens, the seminal vesicles, the ureters. They very frequently affect glandular hollow formations - the pulmonary cells, as pneumonia, the follicles of the intestinal mucous membrane, - almost equally often the parenchyma of the lymphatic glands, fungoid bones or sections of bones, etc.