This proved to Dr. O'Dwyer the need of another {333} instrument (to be employed in the introduction of tubes)--an apparatus by which the mouth could be kept widely open so as to allow of manipulation without undue interference by the patient. For this purpose he contrived the mouth-gag--a very useful little instrument that has been found of service in many other surgical procedures about the mouth besides intubation. His first tubes, however, were not without serious defects. For instance, in order to permit of the extraction of the tube afterward, there was a small slit in the side of the tube, into which the extractor hooked. Into this slit the swollen and edematous mucous membrane was apt to force its way, and (as can readily be understood) in the removal of the tube considerable laceration in the tissues usually was inflicted. Accordingly the tubes subsequently made were without this slit. Moreover, the first tubes that were employed were not quite long enough, a defect which led to their being rather frequently coughed up. This inconvenience was not wholly obviated even by the lengthening of them. O'Dwyer continued his studies, and finally hit upon the idea of putting a second shoulder on the tubes. This, it was hoped, would fit below the vocal cords, and with the cords in between the two shoulders the tubes would surely be retained. This improved tube was actually retained, but the drawback to its adoption (as shown in practice) proved to be that it was retained too tightly. When the time for its removal came it was almost impossible to get it out. It was evident then that some other model of tube would have to be constructed in order to make the process of intubation entirely practical, and thus do away with certain dangers.