- Chemical digestion - The act or process, by which living tissues or cells
take up and convert into their own proper substance the nutritive
material brought to them by the blood, or by which they transform their
cell protoplasm into simpler substances, which are fitted either for
excretion or for some special purpose, as in the manufacture of the
digestive ferments. Hence, metabolism may be either constructive
(anabolism), or destructive (katabolism).