If the opening be small, and be lost both to touch and sight, a second should at once be made, especially in urgent cases, and no time lost in searching for the first. This opening must be made directly in the median line, otherwise the canula will stand awry in the wound and be easily dislodged from its position in the trachea. If the first opening made is faulty in this respect, it is better to at once make a second. It may seem unnecessary to {157} warn the surgeon against thrusting his sharp-pointed bistoury too far inward at the moment of incising the trachea; but as a matter of fact it has been driven through both anterior and posterior walls, and even through the oesophagus, until it has struck the spine. The converse, or a too superficial incision, is an accident more likely to occur, the point of the knife not being made to penetrate the mucous membrane of the trachea, which is probably swollen and thickened. No relief in such cases follows the incision, and an attempt to introduce a tracheal tube may cause it to pass between the mucous membrane and tracheal walls into the submucous tissue, thus stopping up the tube as it progresses. The disastrous result of such an accident can readily be foreseen unless the complication be quickly appreciated as to its nature, the tube withdrawn, and the incision completed. Much more frequently will a somewhat similar accident occur in the operation of tracheotomy for croup or diphtheria. The pseudo-membrane overlying the walls of the air-passage is not penetrated, but pushed before the knife, which has properly incised the walls of the tube; the introduction of the canula now crowds this membrane still farther back toward the posterior tracheal wall, and a complete tracheal stenosis is added to the pre-existing laryngeal one; sudden and urgent dyspnoea follows, and prompt relief alone wards off fatal suffocation. Fortunately, in such instances the forcible efforts at respiration and struggles of the patient are often sufficient to break through the occluding membrane and allow the respiratory current to pass. Violent cough often follows, and more or less of the membrane is forced out through the tube. Should these events not come instantly to pass, the surgeon must not wait for the efforts of the patient, he being often cyanosed and unconscious at this point, but by passing an elastic catheter down through the tracheal tube break through the occluding membrane forcibly. The occurrence of such an accident is always denoted by absence of respiration through the canula and by alarming asphyxia, and its cause needs but little reflection to be appreciated.