=Modified Respiratory Movements.=—The object of coughing is to expel foreign matter from the windpipe or larynx; of sneezing, to clear the nose. The former action consists of a long deep inspiration; the closure of the glottis; a forcible expiration. The blast of air encountering a closed glottis acquires considerable pressure. When the resistance of the glottis is overcome, the blast rushes through, carrying with it mucus or bread-crumb, or whatever the substance may be which irritated the endings of the superior laryngeal nerve. In sneezing, the back of the tongue is thrust against the palate, closing the aperture of the fauces. Inspiration is prolonged. A strong expiration follows. The blast rushes through the nasal cavities. This reflex is usually provoked by a tickling of the endings of the fifth nerve in the nasal mucous membrane. It is also caused in many persons, through the optic nerve, by a bright light; an apparently purposeless reflex about which we shall have something more to say in a subsequent chapter. Laughing and crying are modified respiratory movements as useless, so far as any immediate purpose is accomplished, as sneezing in response to a bright light. As means of expressing emotions they have been cultivated by the human race. Possibly a case for crying might be made out on physiological grounds. Under certain circumstances it relieves a feeling of distress which, while it lasts, is detrimental to the proper functions of the body. Laughing undoubtedly is beneficial. The rapid movements of the chest quicken the circulation. The shaking of the midriff favours the discharge of digestive secretions, accelerates the movements of the alimentary canal, and generally is beneficial to digestion. But “laugh and grow fat” is not necessarily the order of cause and effect. An efficient digestion and a good capacity for assimilation lead to a sense of _bien-être_ which predisposes to a merry view of life. Yawning is a deep inspiration with open mouth and larynx. It commences usually at the end of a normal inspiration, a slight pause being followed by further inspiration, deep and prolonged. Its commencement seems to be due to impulses generated by the relaxation of the tone of the muscle which holds up the lower jaw. The masseter goes off duty for a moment, allowing the jaw to fall. A reflex contraction of the muscles which open the mouth immediately follows. Muscles of the neck and head also come into play. Not improbably the yawn ends in a general stretch. If the origin of this reflex is obscure, its usefulness is marked. The circulation is quickened, the blood is changed, nervous system and muscles again become alert.