METABOLISM (from Gk. perafio?,ijonctabolt', change, from yer(062:iew, mctaballein, to change, from 'Ifni, meta, beyond + 13cl7aetv, ballein, to throw). The continual molecular or physico chemical changes taking place in the protoplasm of organisms, during growth and throughout life. Upon it the life-processes rest. Verworn says that it is solely a process that distinguishes the living organism from the dead organism, and not front inorganic substance; it occurs also among inorganic bodies. Verworn defines it as the thing in which the living organism differs from the lifeless, and says that it consists in the con tinual self-decomposition of living substance, the giving off to the outside of the decomposition products. and, in return, the taking in from the ent-dde of certain substances, which give to the organism the material with which to regenerate itself and grow by the formation of similar groups of atoms, i.e. by 'polymerization.' This is characteristic of all living substance. During the process of metabolism the living cell-sub stance is being continually broken down and reformed by the continual giving off and taking in of material. The metabolism of living sub stance, says Verworn, upon which all life is based. is conditioned by the existence of certain
very labile compounds, which stand next to the proteids and on account of their elementary significance in life are best termed `hiogens.' Their continual decomposition and reformation constitute the life-process.
In plant physiology the term metabolism is used in essentially the same sense as in animal physiology. Two series of processes are distin guishable: (11 Processes which result in the up building of complex substances, particularly such as contain a greater amount of potential energy than the ones from which they are constructed. These processes are designated as 'constructive' metabolism or 'anabolism.' (2) Processes which result in the decomposition of complex substances into simpler ones. designated as 'destructive' metabolism or 'katabolism.' For special discus sions of metaholie processes see ASSIMILATION IN DIGESTioN IN PLANTS; FERMENTATION; NETRITION; PIloTOSYNTIIESI5; RESPIRATION IN PLANTS. Consult Verworn, General Physiology: in outline of the Science of Life (New York, 1599).