Resulting Lesions. In any case of invagination it must be noted that it is not the intestine alone which slips into its fellow, but it carries with it its attaching mesentery, which, dragging on one side of the invaginated gut, shortens and puckers that and turns its opening against the wall of the enclosing gut so as to block it, while the opposite or free side passes on and tends to form convolutions. If the outer and enveloping intestine is too small to allow of this, the detaining mesentery of the invaginated mass must be torn or stretched unduly and its circulation and innervation correspondingly impaired. When the invagination occurs of one portion of the small intestine into another of nearly equal size, the resulting mass is firm like a stuffed sausage, and this enlargement and consolidation ends abruptly at the point of visible entrance of the smaller contracted portion, into the larger dilated one.
If recent, the invaginated mass is still easily disengaged from the enveloping portion, though considerably congested and dark in color in proportion to the duration of the lesion. When it has been longer confined the incarcerated portion is the seat of extreme congestion, and extravasation, and has a dark red or black color. The exudation into its substance, which is especially abundant in the mucosa and submucosa, produces a thickening which may virtually close the lumen, and on the opposing peritoneal surfaces leads to adhesions which prevent the extraction of the imprisoned mass. The interruption of the circulation and the compression of the invaginated mass, leads soon to necrosis and thus a specially offensive odor is produced, and if the animal survives the whole may be sloughed off and passed with the fæces, the ends of the intussuscepted portion and of that receiving it meanwhile uniting and becoming continuous with each other.
Symptoms. These are the violent colic of obstruction of the bowels, soon complicated by those of enteritis and finally of septic infection.
The animal looks at his flank, paws, kicks with his hind feet, lies down, rolls, sits on his haunches, waves the head from side to side, and sometimes eructates or even vomits. Straining may be violent, with the passage of a few mucus-covered balls only, and rumbling may continue for a time if the small intestines only are involved.
The partial subsidence of the acute pains, the presence of tremors, dullness and stupor, the coldness of the ears and limbs, the small, weak or imperceptible pulsations, the cold sweats, dilated pupils, and loss of intelligence in the expression of the eye and countenance may indicate gangrene, and bespeak an early death which may take place in seven hours.
The subsidence of the acute symptoms with improvement in the general appearance and partial recovery of appetite may indicate a spontaneous reduction of the invagination, an issue which may happily arrive in any case in the early stages, but especially in those implicating the cæcum and colon.
An absolutely certain diagnosis is rarely possible, unless the lesion is a protrusion of the rectum, or unless as the disease advances the invaginated part is sloughed off and passed per anum.
Treatment. The failure to make a certain diagnosis usually stands in the way of intelligent treatment. Oleaginous laxatives and mucilaginous gruels are advised to keep the contents liquid, and favor their passage through the narrowed lumen of the invaginated bowel. In cases implicating the floating colon and rectum abundant watery or mucilaginous injections may assist in restoring a bowel which has not been too long displaced. In case of eversion of the rectum, the hand should be inserted into the protruding gut and carried on till it passes through the sphincter ani. Then, by pushing it onward, the arm carries in a portion of the invaginated gut and usually of the outer portion next to the anus as well, and this should be assisted by the other free hand, and even if necessary by those of an assistant, and whatever is passed through the sphincter should be carefully retained, while the arm is withdrawn for a second movement of the same kind, and this should be repeated until the whole protruding mass has been replaced.
Invaginations situated more anteriorly and which can be correctly diagnosed by rectal exploration or otherwise, will sometimes warrant laparotomy, especially those of the cæcum into the colon, where adhesion of the peritoneal surfaces is less common or longer delayed. The patient should be given chloroform or ether, the abdominal walls should be washed and treated with antiseptics, and the incision made back of the sternum and to one side of the median line, and large enough to admit the exploring hand. It has also been suggested to introduce the hand through the inguinal ring, or behind the posterior border of the internal oblique muscle.