We are acquainted with a catarrhal (erythematous) and a croupy form of inflammation, and, on account of the prevalence of a dyscrasic type, we may consider the typhous and the dysenteric processes occurring in the intestinal mucous membrane as allied to the latter.

a. Catarrhal inflammation - or in a lower degree mere catarrhal irritation, catarrh - presents itself as genuine entero-catarrhus, with a discharge of a thin muco-serous secretion in catarrhal diarrhoeas, namely, as a consequence of suppressed cutaneous exhalation. It may result from mechanical or chemical irritation of the intestinal mucous membrane by foreign bodies or stagnating fecal matter; it may also be developed in consequence of congestive or venous stasis in the portal system; or, lastly, it frequently shows a specific, contagious property (exanthematic, typhoid catarrhs), and appears as a precursor of these processes or associated with them, and in the vicinity of morbid growths.

Catarrh is either acute or chronic, and it either attacks the mucous membrane uniformly, or is developed mainly in the villi and follicles.

The anatomical signs of the acute form are, more or less intense redness and injection of the mucous membrane, affecting its entire surface, or appearing as punctiform reddening from affection of the villi, or as a vascular halo surrounding the follicles; relaxation of the tissue, and intumescence of the mucous membrane, equally affecting the entire substance, or only the villi and the follicles, opacity of the mucous membrane and its epithelium from infiltration of the former, and softening of the latter; friability and softening of the mucous membrane. The submucous cellular tissue is injected, relaxed, and infiltrated with a watery, opaque fluid; the secretion is at first copious and serous; as the affection increases in intensity, the former diminishes in amount, becomes opaque, viscid, and puriform.

Chronic inflammation is characterized, in addition to the above signs, by a dark, rusty, livid discoloration, which in severe cases appears to pervade the entire mucous membrane; by a tumid state of the mucous membrane and its follicles, accompanied by increased density of the tissue, copious secretion of an opaque, grayish-white, or yellow puriform mucus.

Acute inflammation frequently passes into resolution, but it often recurs, and may, if the predisposing cause is not got rid of, become habitual or chronic. Chronic inflammation rarely admits of a complete cure. It is generally followed by a blennorrhoic condition; and we thus find, in well-marked cases, a permanent dilatation of the vessels established, with the following alteration in the tissues:

A brown, slate-colored, or bluish-black discoloration of the mucous membrane (deposit of pigment,) involving its entire thickness, or the villi or the follicles only;

Increase of substance, or permanent tumefaction of the mucous membrane, its follicles, or villi, with increased density and consistence (hypertrophy), giving rise in higher degrees to elongation of the membrane, and formation of folds and polypi;

Hypertrophy of the submucous cellular tissue and the muscular coat;

Profuse secretion of a grayish-white and milky, or of a transparent gelatinous and viscid mucus (pituita vitrea).

Catarrhal inflammation occasionally passes into suppuration and ulceration. This is found to occur in consequence of frequent relapses of acute inflammation, but more particularly when an acute attack supervenes upon an existing chronic affection, or invades a blennorrhoic mucous membrane. The mucous membrane is converted into a dark-red, granulated and friable tissue, on the surface of and within which suppuration is established. This penetrates to the deeper tissues, and thus gives rise to abscesses, which open internally; in either case loss of substance is entailed, which increases with more or less rapidity; ulcers follow, which are surrounded by tumid, irregular, sinuous, undermined edges, having a granulating base, and extending into the surrounding cellular tissue or into the hypertrophied muscular coat. The suppuration may even pass through the latter by means of sinuses, in the vicinity of which the mucous membrane presents the above-described appearances, or is blennorrhoic, and often covered with polypous excrescences. This process is invariably accompanied by corrugation and slaty or bluish-black discoloration of the intestinal coats. Catarrhal phthisis thus occasions a contraction of the intestinal canal, which becomes more considerable after the cure of the former. Cicatrization is effected by a dense, resisting cellulo-fibrous tissue, which compresses the mucous membrane in the vicinity of the loss of substance, or the solitary insular remnants of the mucous membrane, into plicated polypous tumours.

The seat and extent of the catarrhal inflammation and of the blennorrhea, differ according to the cause. They are frequently spread more or less uniformly over the entire intestinal tract; they are often limited to a certain portion of the colon or the small intestine, where they occupy large spaces; or they may occur in one or several small circumscribed spots, in consequence of local irritation. These affections are peculiarly liable to recur as long as the predisposing cause continues; they exacerbate from time to time if chronic, and lead to suppuration. They are not common in the small intestine, their usual seat being certain portions of the large intestine, viz. the caecum and rectum.

A peculiar disease that we must here advert to is ulcerative inflammation of the follicles of the colon, such as we find in lientery, brought on by tedious diarrhoeas. An ulcer results, which is distinguished from the catarrhal ulcer just described, by the shape which it derives from the follicle, and still more by the total absence of reaction, which is brought on by the excessive destruction of tissue, and which produces an atonic and relaxed state of the tissues at the base.

In this disease, which in the dead subject is commonly not observed until it has committed extensive ravages, the follicles are at first tumefied in various degrees, and consequently project as smaller or larger round, conical nodules on the internal surface of the intestine, being surrounded by a dark-red vascular halo. Ulceration now ensues in the interior of the follicle, the small abscess penetrates the mucous membrane within the vascular halo, and a fringed ulcerated opening, of the size of a millet seed appears, which leads to a small follicular abscess with red spongy walls. The ulceration continues, and the follicle is eaten away. The mucous membrane that loosely surrounds the enlarged orifice of the abscess, overlays the exposed submucous tissue. In most cases the hyperaemia of this edge diminishes in consequence of the exhaustion brought on by the discharges; it becomes pale, or is discolored by a deposition of black pigment in its tissue, which gives rise to a slaty appearance. The ulcer is of the size of a pea or a lentil, round or oval, the mucous membrane at the circumference is pale, slate-colored, livid, and much relaxed, the cellular tissue at the base is dull white, anaemic, sanguineous or dark blue. A flabby typhous ulcer of the colon is the only thing that might render the diagnosis uncertain.

At this period a secondary destruction of the intestinal mucous membrane commences, which proceeds with great rapidity. The original follicular ulcer enlarges in every direction, forming sinuses and exposing the pale, lax, muscular coat at its base. Several ulcers coalesce, and we thus frequently find the mucous membrane and its cellular substratum destroyed to a considerable extent and the remaining portion of the mucous membrane pale or slate-colored; there is general anaemia and tabes; and the contents of the intestinal canal consist of the half-digested food mixed up with reddish, semifluid, grumous matters.

We may state it as a rule, that the lower down the original, as well as the secondary process takes place, the more fully they are developed. Hence the most extensive destruction is found to occur in the sigmoid flexure and the rectum. It is always confined to the colon. Occasionally the disease runs a still more rapid course, as in infants at the breast; and it is then accompanied by catarrhal irritation of the small intestine.

On account of the alvine discharges, which are invariably associated with this ulcer, the affection may not inappropriately be termed ulcerative diarrhoea.