Endoscopic ability cannot be bought with the instruments. As with all mechanical procedures, facility can be obtained only by educating the eye and the fingers in repeated exercise of a particular series of maneuvers. As with learning to play a musical instrument, a fundamental knowledge of technic, positions, and landmarks is necessary, after which only continued manual practice makes for proficiency. For instance, efficient use of forceps requires that they be so familiar to the grasp that their use is automatic. Endoscopy is a purely manual procedure, hence to know how is not enough: manual practice is necessary. Even in the handling of the electrical equipment, practice in quickly locating trouble is as essential as theoretic knowledge. There is no mystery about electric lighting. No source of illumination other than electricity is possible for endoscopy. Therefore a small amount of electrical knowledge, rendered practical by practice, is essential to maintain the simple lighting system in working order. It is an insult to the intelligence of the physician to say that he cannot master a simple problem of electric testing involving the locating of one or more of five possibilities. It is simply a matter of memorizing five tests. It is repeated for emphasis that a commercial current reduced by means of a rheostat should never be used as a source of current for endoscopy with any kind of instrument, because of the danger to the patient of a possible "grounding" of the circuit during the extensive moist contact of a metallic endoscopic tube in the mediastinum. The battery shown in Fig. 8 should be used. The most frequent cause of trouble is the mistake of over-illuminating the lamps. _The lamp should not be over-illuminated to the dazzling whiteness usually used in flash lights_. Excessive illumination alters the proper perception of the coloring of the mucosa, besides shortening the life of the lamps. The proper degree of brightness is obtained when, as the current is increased, the first change from yellow to white light is obtained. Never turn up the rheostat without watching the lamp. _Testing for Electric Defects_.--These tests should be made beforehand; not when about to commence introduction. If the first lamp lights up properly, use it with its light-carrier to test out the other cords. If the lamp lights up, but flickers, locate the trouble before attempting to do an endoscopy. If shaking the carrier cord-terminal produces flickering there may be a film of corrosion on the central contact of the light carrier that goes into the carrier cord-terminal.