Asphyxia. When the due aeration of the blood in the lungs by the processes of respiration is interfered with, difficult respiration or dyspnoea is the result, and if relief be not afforded death by asphyxia occurs. Asphyxia may arise from obstruction in the respiratory passages, from paralysis of the muscles of respiration, or from some interference with the supply of oxygen from the surrounding atmosphere. In the development of asphyxia three stages are described: in the first the movements of respiration become exaggerated and the increasingly venous character of the blood causes lividity of surface particularly noticeable in the lips and face; in the second stage general convulsions occur, and finally death is ushered in by the stage of exhaustion in which muscular movement is only manifested in an occasional sighing inspiration, while insensibility becomes complete. In the asphyxia of drowning all three stages are passed through in from two to five minutes; artificial respiration (q.v.) is, however, sometimes successful in effecting restoration many minutes after the apparently complete cessation of the vital functions.