\Dis`as*sim`i*la"tion\, n. (Physics)
The decomposition of complex substances, within the organism,
into simpler ones suitable only for excretion, with evolution
of energy, -- a normal nutritional process the reverse of
assimilation; downward metabolism.
   The breaking down of already existing chemical compounds
   into simpler ones, sometimes called disassimilation.
                                               --Martin.