The thickness of the connective tissue of the part varies immensely; sometimes six layers or even more can be separately dissected, while, again, one only may be found before the sac is exposed. If small and recent, the sac may be recognised by its bluish colour, and by the fact that it is possible to pinch up a portion of it between the finger and thumb, and thus to rub its opposed surfaces against each other. If large and of old standing, it is sometimes so thin as not to be recognisable, or again so enormously thickened, and so adherent, as to be defined with great difficulty. If it is small, _i.e._ when the whole tumour is under the size of an egg, it ought to be thoroughly isolated, and its boundaries everywhere defined. If large, and specially if adherent, the neck alone should be cleared. The sac thus being reached, the external abdominal ring should be clearly defined, and the finger passed into it so as if possible to determine the presence or absence of any constriction in it. If it feels tight, the internal pillar of the ring should then be cautiously divided on the finger by a probe-pointed narrow bistoury, in a direction parallel to the linea alba. At this stage the question comes to be considered as to whether the sac should or should not be opened. Much has been said and written on both sides. Not to open the sac avoids the risk of peritonitis, and of injury to the bowel; but, on the other hand, exposes the patient to the danger of the hernia being returned unreduced; for in many cases the stricture is to be found in the sac itself, and adhesions very rapidly form between coils of intestine in the sac and the inner wall. Again, not to open the sac prevents us from discovering the condition in which the bowl is; it may possibly be gangrenous, in which case such a return _en masse_ would be almost necessarily fatal. A general rule or two may be given here:-- 1. The sac should be opened in every case where there is any reason for doubt about the condition of the bowel, where there has been long-continued vomiting, or much tenderness on pressure. 2. Even in cases in which there is every reason to believe the bowel is perfectly sound, the sac should be opened, unless the whole contents can be easily and completely reduced out of the sac into the belly, as in cases where this cannot be done there probably exist either a stricture in the neck of the sac itself, or adhesions of the bowel to the sac. We should endeavour to avoid opening the sac in cases of old scrotal hernia of large size, where the symptoms have not been urgent, especially in large unhealthy hospitals, as the risk of peritonitis is so great. Antiseptic precautions seem considerably to diminish the risk of opening the sac.