Invagination or intussusception,1 incorrectly termed volvulus, consists in the inversion of a portion of intestine into the cavity of the adjoining upper or lower portion.

We frequently find intussusception in the corpses of children and adults, but in the majority of these cases it is produced during the last moments of life, during the death-struggle. It is the result of an unequal irritability of the intestine, and the consequent irregularity of its movements, and it is therefore frequent in diseases characterized by torpor of the cerebro-spinal system, and in the mortal agony proceeding from them; whereas it rarely or never occurs in diseases accompanied by, or ending with, abdominal paralysis such as cholera, typhus, general peritonitis, etc. In this case we find no traces of reaction, the parts are easily restored to their proper relations, the inversions are found occurring simultaneously at several points, though only in the small intestine, and the inversion may take place downwards, and at the same time, but rarely, upwards.

Another form of invagination, which, once formed, presents itself as an idiopathic, dangerous, and often fatal disease of the intestinal tube, is of extreme importance, and will be the subject of the following remarks.

Every intussusception consists of three layers of intestine: of these, reckoning from without inwards, the first and second present their mucous, the second and third their peritoneal, surfaces to one another. The canal of the intussusception or volvulus passes through the latter. In order to facilitate comprehension, and in accordance with fact, we term the external layer of the intestine the sheath of the volvulus, or the intussuscipient portion, the innermost layer the entering tube, the middle one the receding or inverted tube, and the last two together, the intussuscepted portion, or the volvulus properly so-called. It follows that isonomic layers are always opposed to one another; and we shall find this to be the case even when the intussusception is double, and consists of five superimposed layers.

1 Oestr. Jahrb. xiv. 4.

Between the entering and inverted tube we find a portion of mesentery, of corresponding size, and of an arcuate form. It is folded up so as to represent a cone, the apex of which lies at the free termination of the volvulus, with its base in the sheath, and at the entrance to the invagination.

This portion of mesentery is always in a state of tension, which chiefly affects the part belonging to the inverted tube, and has a singular influence upon the form of the volvulus. It is the cause of the following circumstances:

Firstly; that the volvulus does not lie parallel to its sheath but always offers a greater curvature than the latter, the inverted tube being compressed in its concavity into tense transverse folds.

Secondly; that the orifice of the volvulus does not lie in the axis or in the centre of the sheath, but external to it; and that, following the traction exerted upon it by the mesenteric fold that belongs to the inverted intestine, it is directed towards the mesenteric wall of the sheath; that it is not circular, but represents a fissure. This affords a diagnostic sign for the examination of intussusceptions of the rectum, which are within the reach of manual exploration.

Intussusceptions occur with equal frequency in the colon and small intestine; but several cases which have been described as occurring in the former are remarkable on account of the magnitude they attained. In these cases the sheath contains a very long portion of the colon and ileum; both may be inverted two or three times, and the intussuscepted part advances to the vicinity of the anus.

An inversion of the intestine from above downwards is the most usual occurrence. Post-mortem examinations have, with very rare exceptions, proved this to be the case; and it is but fair to assume the same in those cases in which, after urgent symptoms of danger, larger or smaller portions of intestine were discharged, and the patients recovered.

We naturally ask how the intussusception is brought about, and how its enlargement is effected?

The cause is to be found either in the contraction and movability of a piece of the intestine, on which account it passes into the adjoining and more capacious tube; or in the extreme expansion or relaxation of a segment of intestine, which gives rise to an inversion of the adjoining narrower and more innervated portion. In every case the volvulus is formed at the expense of the external layer of the intestine or sheath. For we find that the entering portion, as it enters and advances (increase of the volvulus), is not reverted at its free termination to form the receding tube, but that the latter is formed by the inversion of the sheath at the entrance of the volvulus.1

Whether the intussusception takes place in one way or the other, the volvulus is not immediately subjected, as is commonly thought, to annular strangulation. In the first instance, the mesentery of the volvulus and its vessels suffer tension and compression at their entrance into the sheath; and, in consequence, we have in the volvulus an obstruction to the circulation, with swelling and intense redness, in short, violent inflammation, which gives rise to sero-sanguineous infiltration of the tissues, plastic effusion on the contiguous serous surfaces of the entering and receding tube, and upon the mucous membrane of the latter. The inverted portion is invariably the one that suffers most; the inflammation of the entering tube is less considerable, and it is characteristic, that even when the inflammation of the volvulus runs high, its mucous membrane remains pale; the sheath of the volvulus also is but slightly affected in small intussusceptions, with the exception of the peritonitis at the point where it enters. In large invaginations of the intestine, however, the sheath is more deeply involved in the inflammatory affection on account of the tension of the mesentery and the strangulation of the vessels.

1 [In other words, the volvulus increases at the expense of the inferior portion of the intestine. - Ed].

In consequence of the tumefaction that results from the inflammation of the volvulus, we find, as a secondary occurrence, the formation of a true annular incarceration, either at the entrance, or in rare cases, at other points.

During this period, in which the volvulus becomes fixed, in consequence of the tumefaction, the incarceration, and even the adhesion of the contiguous serous surfaces, which is brought about by plastic exudation, it gradually or periodically enlarges to an enormous extent; the peristaltic action, and the increased accumulation of the intestinal contents, forcing the volvulus, the sheath of which continues to be progressively inverted, lower down. We are thus led to distinguish between a primary and a consecutive form.

If the intussusception does not prove fatal by the peritonitis which extends upwards from the serous surfaces of the entering and receding tube, with symptoms of strangulation, or by gangrene of the volvulus, it may have other more or less favorable terminations.

a. The most favorable issue, although purchased at the greatest risk of life, is gangrene and discharge of the volvulus and its mesenteric portion, subsequent to a complete adhesion between the entering and receding tube at the entrance into the sheath. At the spot where the separation has taken place, we find, in the corpses of individuals who had been thus affected, an annular swelling, which more or less interferes with the calibre of the intestine, and adhesions with the contiguous peritoneal surface, and more particularly of the mesentery.

b. In rare cases, in which the incarceration has been developed at an unusual point, only a partial sloughing of the volvulus takes place, and the portion which lies above the strangulation is retained. Under these circumstances, the latter forms a conical plug with a narrow channel, and projects into the cavity of its sheath, surrounded by a thick fringe of mucous membrane.

c. Occasionally the inflammatory action which has taken place in the volvulus abates, after having caused adhesion between the entering and receding tube, and the volvulus is retained.

The process described under a, generally leaves a sufficient passage, and consequently ends in a permanent cure, which cannot be predicated of the other two events. In the latter, a chronic state of hyperaemia and inflammatory intumescence remain, with a liability to exacerbations. General intestinal inflammation not unfrequently follows. The channel of the intestine does not suffice for the removal of its contents, and the volvulus, or the remainder of the volvulus, are moreover the cause of a consecutive increase of the intussusception.

Invaginations occur at all ages. Diarrhoea is the chief predisposing cause, and the most rational therapeutic proceeding consists, according as the inversion has taken place upwards or downwards, in an early injection or exhaustion of air by means of a syringe. To be effective, this must be done before the volvulus has formed adhesions.