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. --Dunglison.
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
intrussusception. --McKendrick.