Metabolism, or Metastasis, the stoffwechsel of German physiological writers, is a general name for all the changes which take place within an organism from the first taking in of food to its resolution into the products of excretion or decomposition. It thus includes assimilation and protoplasmic growth, the chemical processes which generate bodily energy and build up new structures, and the breaking up of complex organic substances into such simple substances as water, urea, ammonia, or carbon-dioxide. These processes of constructive metabolism, o.nabolism (q.v.), or life, and of destructive metabolism, Itatabtilism (q.v.), or death, are constantly going on side by side within the body, and there is some evidence of their alternation in a momentarily explosive manner in the protoplasm of each living cell.