or properly disposed of in a suitable container it is to be understood that the present invention is not limited to the embodiments described above but encompasses any and all embodiments within the scope of the following claims it will be apparent that tension spring 84 may be replaced with a compression spring if the circular aperture 64 is moved from the distal end of slot 62 to the proximal end of slot 62 however this would bias blade 30 in the cutting position normally and require the blade 30 to be locked in the retracted position which for safety reasons is not preferred it will also be apparent to those skilled in the art that considerable simplification in parts may be achieved if spring 84 is made nonremoveable in that event one end of spring 84 may be rigidly attached to an interior wall extending transversely in the proximate section 12 of handle 10 cylinder 80 might be replaced with a rod to which the other end of spring 84 is rigidly attached with or without a stop means between the proximal 12 and distal 16 sections of handle 10 to limit the travel of the blade holder with such an arrangement end cap 92 need not be threaded but may secure to the proximal end of the handle 10 by detents in order to be removable and replaceable by a handle extension also the proximal portion of the handle might then be rectangular in shape to suit the preference of the physician the essential advantages of the present invention including an ergonomically shaped button 70 for retracting the blade 30 placed in a convenient location on the handle 10 not likely to be accidentally disturbed during use.