in medicine, the act of voiding the excrements by the anus.—When the feces are accumulated in the intestinum rectum in insufficient 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 compelled on all sides, the resistance of the sphincters is overcome, and the feces 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 dyfenteries, for instance, that the feces are very thin, and have considerable acrimony; and then the irritation they occasion is more frequent, so as to promote their discharge without any prelude from the diaphragm or abdominal muscles; and sometimes involuntarily, as is the case when the sphincters become paralytic.