DEJECTION, in medicine, the act of voiding the excrements by the anus.—When the faeces are accumulated in the intellinum rectum * in sufficient quantity to become troublesome either by their weight or acrimony, they excite a certain uneasiness, which produces an inclination to go to stool. The efforts for this purpose are begun by a considerable inspiration, in consequence of which the diaphragm is carried down towards the lower belly; the abdominal muscles are at the same time contracted in obedience to the will; and the intestines being compressed on all sides, the resistance of the sphincters is overcome, and the faeces pass out at the anus; which is afterwards drawn up by its longitudinal fibres, which are called levatores ani, and then by means of its sphincters is again contracted: but it sometimes happens, as in dysenteries, for instance, that the faeces are very thin, and have considerable acrimony; and then the irritation they occasion is more frequent, so as to promote their discharge without any pressure from the diaphragm or abdominal muscles; and sometimes involuntarily, as is the case when the sphincters become paralytic.