1 - We define internal hernia, in contradistinction to external hernia, as a change of position in the intestine leading to incarceration, which occurs in the abdominal cavity without the formation of a hernial sac, and which is therefore not accessible to the usual mode of examination applicable to external hernia. Certain cases in which the intestine is placed or incarcerated in congenital folds or pouches of the peritoneum, such as we occasionally see in the hypogastric region, are to be viewed as transition forms between internal and external hernia (vid. Peritoneum, p. 24). The former are also termed incarceration strangu-latio interna.

They may be subdivided in the following manner: a. Incarceration is the result of the simple pressure, which is exerted upon one or more points of the intestinal tube, by a portion of the intestine or by the mesentery, resting upon the former. It is a matter of course that this simple compression of a portion of the intestine, can only be effected in the direction of the resisting posterior walls of the abdomen, and at its lower segment; inasmuch as the occurrence of a similar relation anteriorly is inconceivable, on account of the smoothness and yielding nature of the parts. Experience confirms the fact that the small intestine, from repletion or increase of volume, is particularly prone to occupy abnormal positions; it is very liable to descend, and with its lengthy and frequently hypertrophied mesentery, fall and weigh upon the colon or the rectum, and to compress their walls.

These incarcerations of the intestine commonly occur at an advanced age, at which a descent of the intestines to a lower region of the abdomen and into the pelvic cavity, prolapsus of the pelvic viscera and large herniae, which may be viewed as analogous conditions, are very frequent.

A long, flabby mesentery predisposes to the complaint; especially when, by traction, it has been converted into a pedicle or cord. Repletion of the intestine above a stricture, accompanied by atony, or the dislocation of the intestine in large herniae (inguinal and scrotal herniae), is likely to produce this effect.

b. Incarceration may be the consequence of a rotatory movement, and of this there are three varieties: a. A portion of intestine may have become twisted upon its own axis, and we then find that even semi-rotation causes such an approximation of its parietes, that they touch and close up the passage. This can probably only occur in the colon, and according to the cases on record, only in the colon ascendens. Accumulations of gas, and unequal filling of different portions of the intestine, appear, as far as we are able to judge from the few cases which have been noticed, to be the cause. Such an occurrence is scarcely conceivable in the small intestine, on account of the uniformity of its calibre, the absence of angular flexures, and its loose position, as every rotation of one portion upon its axis would be counterbalanced by the rotation of the next segment.

1 Vide Oestr. Jahrb. x. 4.

ft. The mesentery may be the axis, and the intestine will then be rolled up upon the former, i. e., the entire mesentery, or a portion of it, is twisted into a cone, and in proportion to the number of its rotations, more or less of the intestine will be dragged after it. In this case we must take into consideration the traction and the pressure, which the intestine suffers at the acute angle, which the dependent mesenteric cone forms with the base whence its point rises. This variety can scarcely occur anywhere but in the small intestine and its mesentery.

y. One portion of the intestine, either single or double - a coil - may afford the axis round which another portion with its mesentery is thrown, so as to be throughout in contact with the circumference of the axis, and thus to compress it like a ferrule. This variety is evidently a higher degree of the first in which a portion of intestine is merely compressed from before backwards, and, as it were, flattened down. A coil of small intestine, the sigmoid flexure, or the caecum, may form the axis.

The last two varieties occur like the first, chiefly at an advanced period of life. In early life a predisposition to the affection may be caused by a congenital malformation of the mesentery, by large herniae, or by small herniae when there is adhesion of the intestine.

This predisposition consists, first, as in the incarcerations of the first variety - in a congenital or acquired long, loose, and flabby mesentery, by which a rotation of the intestine round the mesentery or another portion of intestine is rendered possible; and secondly, in an enlargement of the abdominal, and especially of the pelvic, cavity.

c. The incarceration of the intestine may be effected by peculiar structures, which either belong to the normal condition, or are congenital malformations, or are, in part at least, the products of previous morbid processes. We allude to genuine incarcerations of the intestine in various annular spaces or fissures, of which we cite the following: a. The fissure of Winslow, in which we once found a large portion of small intestine strangulated; ft. An intestinal diverticulum (verum), which is directly or indirectly, by means of an obsolete vascular cord, attached to a certain portion of the peritoneum; y. Adhesions of the free end of the caecum, or of the vermiform process; d. Holes or fissures (congenital or acquired) in the mesentery; e. Malformations of the omentum, forming rounded or flattened cords and bands which are attached to the peritoneum, or furcated fissures of the omentum; c Pseudo-membranous formations, as the result of previous exudative processes, in the shape of cellular or ligamentous cords, bands, or plates, which pass from one part of the intestine or the mesentery to another, from the intestine to the abdominal parietes, the omentum or an organ of the abdominal and pelvic cavity, or from one of these to the abdominal parietes, or between the organs themselves.

It is most frequently a portion of the small intestine which is incarcerated in these structures; only the more movable portions of the colon, the caecum and the sigmoid flexure, are likely to become involved.

These varieties of incarceration are very common, and, as compared with the others, the most frequent.

They occur at every period of life. The female sex is more prone to them than the male, as the omentum, the diverticula that may be present, and pseudo-membranous formations, are not only frequently attached to the internal sexual organs of the female, but the latter are themselves liable to give rise to new growths.

The consequence of internal hernia is a distension of the intestine above the compressed or strangulated portion, peritoneal inflammation, paralysis, and ileus; the incarcerated portion in hernia of the third variety is from the strangulation of its mesenteric vessels peculiarly liable to congestion and gangrene.

This affection, when diagnosed, most imperatively requires an operative proceeding, for the purpose of disentangling and arranging the intestines, and for division of the strangulating structures with or without the knife.