=Invagination= is here used to express the entrance of one entire division of the bowels within another. In this sense it is chiefly witnessed upon the large intestines; whereas intro-susception is mostly present upon the smaller bowels. The mesentery must be ruptured before such an accident can take place; but then the agony attendant upon the previous derangement is so powerful that it is impossible for the hugeness of this lesion to increase the violence of the torture; nor is there any sign by which so sad a catastrophe can be predicated. Before =strangulation= can possibly occur, the mesentery must be sundered. It almost always happens to a portion of the small intestines. The bowel, freed from its support, soon involves itself with numerous complications; or the rent membrane may twine round a knuckle of the gut. [Illustration: A KNUCKLE OF INTESTINE STRANGULATED BY THE RUPTURED MESENTERY.] [Illustration: RUPTURE OF THE SMALL INTESTINES.] The above illustration, however, shows one of the simplest forms in which the accident can possibly take place; but no person, however acute, could distinguish between strangulation from rupture of the intestines. The last generally occurs upon the smaller bowels, and happens to the interspaces upon the superior portion of the tube, between the vessels which nourish the digestive canal. The ingesta, is consequently forced between the layers of the mesentery. The most intense anguish, inflammation, and death are the consequences. [Illustration: THE SAC FORMED IN THE BOWEL; THIS THE CALCULUS HAS QUITTED, WHILE ANOTHER PORTION OF THE INTESTINE HAS SO FIRMLY GRASPED IT AS TO RUPTURE ITSELF. ]