Rigid instruments have one advantage over flexible ones, in that their points can be guided by the surgeon; the points of flexible instruments cannot be directed, hence the introduction of the latter into a stricture is less easily managed, consequently bougies with various kinds of points should be kept. But flexible instruments cause far less irritation than rigid ones, and should always be employed instead of the latter when possible: with patience and practice much of the difficulty attending their introduction is overcome. The French bougies, with tapering ends and bulbous points, slip more easily through a stricture than instruments having the same diameter throughout, and bougies with fine tapering points can sometimes be introduced where others fail. _Passing Catheters._—In passing instruments along the urethra the conformation of its interior should be borne in mind. From the meatus to the triangular ligament, the normal urethra, when gently stretched, becomes a straight tube; having, nevertheless, just within the meatus, a pouch in the roof, the lacuna magna, where the point of the instrument may catch if not turned downwards. At the bulbous part the urethra enlarges in capacity by having a slight downward curve in its floor, just before the triangular ligament is reached. In this depression, the beak of the catheter is apt to sink below the level of the passage through the ligament, which is always a fixed point. Beyond the triangular ligament the urethra curves gently upwards, has a floor beset with irregularities, in which the point of the instrument easily catches, if not raised as it passes along the curve.