the reception of one part within another.-the abnormal reception or slipping of a part of a tube, by inversion and descent, within a contiguous part of it; specifically, the reception or slipping of the upper part of the small intestine into the lower; introsusception; invagination.-the interposition of new particles of formative material among those already existing, as in a cell wall, or in a starch grain.-the act of taking foreign matter, as food, into a living body; the process of nutrition, by which dead matter is absorbed by the living organism, and ultimately converted into the organized substance of its various tissues and organs.