"insertion space" for any other instrument. Until all of these points are determined it is a grave error to insert any kind of instrument. If possible even swabbing of the foreign body should be avoided by swabbing out the bronchus, when necessary, before the region of the intruder is reached. When the operator has determined the instrument to be used, and the method of using it, the instrument is cautiously inserted, under guidance of the eye. [160] _The lip of the bronchoscope_ is one of the most valuable aids in the solution of foreign-body problems. With it partial or complete version of an object can be accomplished so as to convert an unfavorable presentation into one favorable for grasping with the forceps; edematous mucosa may be displaced, angles straightened and space made at the side of the foreign body for the forceps' jaw. It forms a shield or protector that can be slipped under the point of a sharp foreign body and can make counterpressure on the tissues while the forceps are disembedding the point of the foreign body. With the bronchoscopic lip and the forceps or other instrument inserted through the tube, the bronchoscopist has bimanual, eye-guided control, which if it has been sufficiently practiced to afford the facility in coordinate use common to everyone with knife and fork, will accomplish maneuvers that seem marvelous to anyone who has not developed facility in this coordinate use of the bronchoscopic instruments. _The relation of the tube mouth and foreign body_ is of vital importance. Generally considered, the tube mouth should be as near the foreign body as possible, and the object must be placed in the center of the bronchoscopic field, so that the ends of the open jaws of the forceps will pass sufficiently far over the object. But little lateral control is had of the long instruments inserted through the tube; sidewise motion is obtained by a shifting of the end of the bronchoscope. When the foreign body has been centered in the bronchoscopic field and placed in a position favorable for grasping, it is important that this position be maintained by anchoring the tube to the upper teeth with the left, third, and fourth fingers hooked over the patient's upper alveolus (Fig. 63) _The Light Reflex on the Forceps_.--It is often difficult for the beginner to judge to what depth an instrument has been inserted through the tube. On slowly inserting a forceps through the tube, as the blades come opposite the distal light they will appear brightly illuminated; or should the blades lie close to the light bulb, a shadow will be seen in the previously brilliantly lighted opposite wall. It is then known that the forceps are at the tube mouth, and the endoscopist has but to gauge the distance from this to the foreign body. This assistance in gauging depth is one of the great advances in foreign body bronchoscopy obtained by the development of distal illumination.