But it is unnecessary to resort to an expla nation which might prove so practically dan gerous, because the existence of strangulation with all its fearful sequelw may be proved, in situations and under circumstances where the influence of spasm or of muscular action is ob viously impossible. Thus intestines have been found strangulated within the cavity of the ab domen itself, as when a fold of intestine has passed through an accidental opening in the mesentery or the omentum, or when artificial bands or nooses have been formed by lymph, the products of former inflammation. Scarpa relates a very interesting case in which he fbund that the appendix vermiformis surrounded in the manner of a ring and strangulated a long loop of the ileum just before its insertion into the colon.
If it be conceded that the natural openings at which abdominal hernim occur are composed either of tendon or of tendon and of bone, and therefore are not subject to accidental variations of size from irregular muscular action, it would seem on a prima facie view that wherever any substance had passed out it ought to be able to return, provided an equal degree of force is employed with that which originally caused the displacement. And this actually does take place, for the hernia returns spontaneously or is easily reduced as long as the original propor tion between the size of the protruded part and that of the aperture remains unaltered. Again, as long as this relation is maintained, the cir culation through and from the protruded viseus will continue equable and healthy, but an in testine from its structure and its functions is extremely liable to a change of size, and when that happens, the proportion no longer exists, and the hernia begins to become incarcerated. If not relieved, the protruded viscus continues to swell, and is thus made to form an acute angle at the spot where it escaped, which tightens the ring of intestine immediately at the neck of the sac : the return of the venous blood is thus prevented ; the swelling then increases until not even gas can pass through, and then strangulation is complete. In this way a number of circumstances connected with hernia can be explained. If the ring is small, a very trifling change of size in the protruded part will be sufficient to cause strangulation : hence cniml hernia is more liable than inguinal, and very recent ruptures in which the ring is of its natural size than those of long standing, in which that aperture is probably enlarged.
Persons who are formed with large rings, and thus possess an hereditary dispnsition to hernia, are less liable to strangulation : this may ex plain Pott's remark that " if the hernia be of the intestinal kind merely, and the portion of the gut be small, the risk is the greater, stran gulation being more likely to happen in this case;" for assuredly if the ring is so small as to permit only the escape of a knuckle of intestine, a very trifling change in the latter will be suffi cient to establish a disproportion between them. Again, if a hernia has come down, and been reduced, and kept up until the neck of the sac has been diminished in size, and if afterwards a protrusion takes place, a very trifling alteration in this latter will render it incapable of return, and explain why such her nia: are so frequently strangulated at the neck of the sac. llence it appears that a straitness or tightness at one of the rings may be a predis posing cause of strangulation, that is, may be a reason why one hernia should become sooner strangulated than another, but the immediate or efficient cause is a change in the condition of the viscus itself. Thus when a loop of in testine is gangrened, and its contents have escaped totally or partially into the sac, the hernia often returns spontaneously, the parts in the immediate neighbourhood of the ring re maining unaltered. Also if such a hernia is the subject of operation, there is no necessity for dilating the seat of the stricture : indeed Louis forbids the practice lest some essential point of adhesion should be destroyed. "Di latation," says he, " is only recommended in order to facilitate the reduction of the strictured parts. In the gangrened intestine there is no reduction to make, and there is no longer strangulation, the opening in the intestines having removed the disproportion that had existed between the diameter of the ring and the volume which the parts had acquired; and the free passage of the excrement which the sphacelus has permitted removes every symptom that depends on the strangulation."* In like manner may be understood why omental her nim are less liable to become strangulated, be cause this structure is not subject to any sud den change of shape or increase of volume : when it does occur, the progress of the disease is more slow, and the symptoms are said to be less severe.