(2) Nose, throat, and tongue operations where intratracheal ether is not available. CHAPTER X INTRATRACHEAL INSUFFLATION OF ETHER Intratracheal insufflation consists in driving a current of air under pressure, through a tube introduced by way of the mouth and larynx, deeply into the trachea. The current of air which is continuous, returns between the tube and the wall of the trachea, and escapes through the mouth and nose. Certain Physical Considerations. The work of Meltzer and Auer has demonstrated that this insufflation of air into the trachea under adequate pressure ventilates the pulmonary alveoli, and enables the normal diffusion of gases to be carried out for many hours, independently of all respiratory movements. If the air in its passage under pressure is made to pass through a chamber containing ether, we are enabled to introduce into the pulmonary alveoli, ether vapour of varying strength, and, by this means, to maintain surgical anæsthesia. * * * * * THE ACTUAL PROCESS OF EXTERNAL RESPIRATION consists in the absorption of oxygen from the alveoli into the blood of the lung capillaries, and the elimination of carbon dioxide from the lung capillaries into the alveoli. The oxygen has to be brought from the outside to the alveoli, and the carbon dioxide has to be conducted from the alveoli to the outside. Between the outside and the alveoli is the long airshaft, consisting of mouth and nose, pharynx, larynx, trachea, bronchi and bronchioles. In natural respiration the conduction of oxygen inwards, and of carbon dioxide outwards, is carried through by a complicated pumping mechanism. In ordinary inhalation anæsthesia, this mechanism is entrusted with the task of introducing ether vapour into the alveoli. In intratracheal insufflation the work of this natural pumping apparatus is taken over by an artificial mechanism. In considering the justification for this, the following points are to be noted:-- (1) The patient is unconscious--not naturally so as in sleep--but unnaturally as the result of drugs; there is therefore a probability that the elaborate natural mechanism may not work smoothly--especially is there a danger that the free airway may be interfered with. Intratracheal insufflation obviates this danger. (2) By means of the artificial mechanism, air is brought with some force to the mouth of the bronchi, and thus a more rapid and more powerful diffusion of gases takes place. (3) The mechanism ensures the maintenance of a current of air blowing forcefully from the trachea and larynx through the pharynx, mouth and nose. This re-current continuous air-stream effectively prevents the entrance of blood or any infectious material into the bronchi and air cells, and thus the danger of septic lung troubles is obviated.