Once asphyxia, especially mechanical asphyxia, has begun, it almost invariably tends to get worse. The engorgement affects among other venules, those which run under the mucous membrane of the respiratory tract, still further obstructing the passage of air. The muscular rigidity, moreover, soon manifests itself in the adductors of the vocal cords and the muscles which close the jaws: the patient has thus entered into a “vicious circle,” Fig. 5. It is evident that the prevention of the earliest signs of asphyxia is to the anæsthetist a matter of vital interest. The cardinal points to watch are as follows:-- (1) Keep the neck of the patient as far as possible in a natural position, _i.e._ do not either flex or extend the head unduly upon the body unless the nature of the operation demands such an unusual position. (2) Maintain a free passage for air either through the nose or the mouth. (3) Keep the lower jaw in good position throughout the administration. (4) Avoid turning the face from the lateral to the dorsal (face up) position unless essential. If it has to be done, be careful first to mop out any “pool” from the dependent cheek. (5) Deal as effectively as possible with the earliest appearance of laryngeal stridor. Let us see how in a normal case, these rules can be applied. With the patient lying (or, in exceptional circumstances, sitting) in a comfortable position, the shoulders and head raised above the rest of the body and the face looking upwards (or straight forwards, in the case of the sitting patient), the anæsthetic is begun slowly, and the patient encouraged to take his time and to breathe naturally. At this stage the jaw needs no support, the muscles being neither relaxed by deep anæsthesia, nor spastic from asphyxia. With the advent of muscular relaxation, the head is turned to one side, that which is opposite to the side on which the surgeon will be working, being usually chosen. We must now determine whether the patient can breathe best through the mouth or the nose, and make sure that the channel chosen is as free as possible. In the majority of cases it will be found that respiration is oral, and that all that is necessary is to support the lower jaw by a finger hooked into the depression just below the symphysis mentes. The hands of the anæsthetist, therefore, take up a position from which in nine cases out of ten they will never require to be moved.