1.The reception of one part within another.
2.(Med.) 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.
3.(Bot.) The interposition of new particles of formative material among those already existing, as in a cell wall, or in a starch grain.
4.(Physiol.) 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. "Dead bodies increase by apposition; living bodies by intussusception."
