the operation of opening the trachea or windpipe (see Respiratory System) and inserting a tube (canula) to provide a means of breathing when the natural air-passage is obstructed. The operation is by no means easy when performed on a small child, for the wind-pipe is deeply placed amongst important structures. The chief anxiety is in connexion with haemorrhage, for the vessels are large and generally overfull on account of the impairment of the respiration. The higher the opening is made in the trachea the easier and safer is the operation.