1. On the intestines themselves; but for all surgical purposes, they are out of our reach. We cannot do more than, by diminishing their contents, diminish their volume, and by position and rest reduce to the utmost their tendency to protrude. This includes the medical and prophylactic treatment of hernia, or rather of the tendency to hernia. 2. We may try what can be done with the _sac_ which the intestines have pushed down before them. Can it be obliterated? If it can, perhaps the intestines may be retained in their cavity. Very many plans of dealing with the sac have been tried. To cause obliteration of its cavity many methods have been proposed:--by ligature of it along with the spermatic cord, involving loss of the testicle, either by gradual separation, by sloughing, or by immediate removal;--by cutting into it, and then stitching it up;--by constricting it with wire, as in the _punctum aureum_; by pinching sac and coverings up, by passing needles under them as they emerge from the external ring, as Bonnet of Lyons did; by constricting sac alone with a double wire, by subcutaneous puncture, as Dr. Morton of Glasgow has done;--by severe pressure from the outside with a strong tight truss and a pad of wood, as proposed by Richter; by setons of threads or candlewicks, as proposed by Schuh of Vienna;--by injection of tincture of iodine or cantharides, as by Velpeau and Pancoast;--by the introduction into the sac of thin bladders of goldbeaters' skin, which were then filled with air, and were intended to excite inflammation, as in the radical cure of hydrocele; or by the still more severe method of Langenbeck, consisting in exposing the sac by a free incision at the superficial ring, separating it from the cord, and passing a ligature round the sac alone, leaving the ligatured portion in the scrotum either to become obliterated or to slough out. Schmucker of Berlin varied this, by cutting away the constricted portion below the ligature. The objections to these methods are various: the more gentle are uncertain and inefficient; of the more severe, some involve mutilation, by the loss or removal of the testicle; others, as those of Langenbeck and Schmucker, are very dangerous and fatal, by the inflammation spreading to the peritoneal cavity (20 to 30 per cent. died); while all of these methods afford at best only temporary relief. And this is only what might have been expected, for the sac was only a _result_ of the protrusion, not a _cause_; and so long as the weakness and insufficiency of the parietes of the abdomen remain, so long will the extensible loosely-attached peritoneum continue to furnish new sacs for visceral protrusions. 3. We have now only the canal left to act upon; and the operations on the canal may be divided into two great classes:-- (_a._) Those in which the operator attempts to plug up the dilated canal. (_b._) Those in which he tries to constrict it, by reuniting its separated sides.