and in the propulsion of the child from the uterus.
The state of the mind considerably af fects the mode of respiration, although the muscles of that function are so far inde pendent of the will, that they act without any exertion of volition, and continue their functions during sleep, when all the vo luntary powers are suspended. When the lover, plunged in a soft reverie, fetches a deep sigh, the physiologist observes a strong and protracted inspiration, follow ed by a similar expiration ; crying and sobbing, differ from sighing only in the circumstance of the expiration being in terrupted, or divided into several distinct periods. In gaping, which is attended with a sense of weariness, there is a large inspiration, accomplished in a gradual manner, and by a kind .of effort; the en trance of a great quantity of air is facili tated by opening the mouth wide : this is followed by a complete gradual expi ration. Sneezing is a strong and violent expiration, and the noise accompanying it is produced by the air passing out with rapidity, and striking against the winding parietes of the nasal fossw. The effort,
which is occasioned by the irritation of the pituitary membrane, is a convulsive motion of the muscles of respiration, and particularly of the diaphragm. In cough ing, the expirations are shorter and more frequent; the expelled air carries off the mucus lodged in the trachea and bron aim, and this discharge constitutes ex pectoration. Laughing is a short inspi ration, followed by several short and ra pid expirations.
The alternate dilatation and contrac tion of the chest, proceed uninterruptedly from the moment of birth to the end of life, and in a healthy adult are repeated about fourteen times in a minute, so that each act of respiration corresponds pretty nearly to five pulsations of the heart. For an account of the changes which the blood experiences in respiration, as well as thipe which take place in the respired air, and for the composition of the blood itself, see