CHAP, ii LIVING MATTER 43 



the result of two opposite processes, which are continually super- 

 posed and succeed each other : a synthetic, assimilative, and con- 

 structive process, known as anabolism, and an analytical, dissimila- 

 tive, and destructive process, known as katabolism. 



In the anabolic process, the cell forms or elaborates organic 

 matter from the nutrient materials, by the aid of energies derived 

 from the environment or developed by oxidation of its own 

 substance ; it takes up this organic matter by intussusception, 

 transforms it into living protoplasm, or stores it as reserve 

 material. 



In the katabolic process, the cell breaks up and uses the 

 reserve materials, disintegrates its own protoplasm, and returns 

 to the environment the products of decomposition, combustion, 

 and activity. 



While the two opposite processes which constitute metabolism, 

 or the exchanges of matter and energy, are intimately connected, 

 they are differently distributed in the two principal phases of life, 

 the progressive and the retrogressive. During the first phase the 

 organism grows and develops, and is active in its functions; 

 during the second, it dwindles and degenerates, and its functions 

 are abated. The characteristic phenomena of nutrition, growth, 

 and development in the organism are the natural consequences of 

 metabolism, where the assirnilatory or anabolic processes prepon- 

 derate ; so, too, atrophy, senility, and death result from predomin- 

 ance of the dissimilatory or katabolic processes, when life is on the 

 wane. 



Between the progressive and retrogressive phases of life, 

 between youth and age, there lies a long intermediate period, 

 during which the two opposite processes, anabolic and katabolic, 

 are practically in equilibrium. This is the phase of maturity, 

 characterised by the full and vigorous exercise of all the vital 

 functions, more particularly of the reproductive capacity. 



It is only when growth and ontogenic development are com- 

 plete that the organism is able to reproduce itself. In other words, 

 only when the factors or hereditary tendencies accumulated within 

 the germ from which the organism has arisen, have become per- 

 fectly developed and active, is it capable of forming by itself or 

 by intercourse with an individual of the opposite sex, new germs, 

 i.e. new aggregates of hereditary elements adapted for reproduction 

 and conservation of the species. 



Metabolism is the invariable physiological basis of these 

 marvellous phenomena : when the anabolic process predominates, 

 the hereditary tendencies contained in the germ develop and 

 become active; when the evolution of the individual is com- 

 plete, the metabolic process is turned to preparing the hereditary 

 material of new organisms. 



II. Metabolism as the exchange of matter between organism 



