CHARACTERISTICS OF LIVING MATTER 5 



ity"; and since growth is the foundational life-process — 

 that by which all living matter is brought into existence 

 — we see at once that the specificity of the underlying 

 metabolic syntheses is the essential condition underlying 

 organic specificity. When constructive metabolism 

 ceases, not only does growth cease but life itself, since 

 the continual formation of specific material is a pre- 

 requisite for normal maintenance. 



Each of the terms above, however, designates a 

 feature or aspect of vital phenomena which is as a 

 rule perfectly definite and distinguishable from the 

 others. Organic growth is perhaps best defined as 

 increase in the quantity of the specifically organized 

 living material.^ Reproduction is the formation of new 

 individuals by growth from the parent organism, or a 

 detached portion of the latter (germ, gamete); in 

 metazoa the replacement of outworn or senescent 

 individuals is thus accomplished. Reproduction has 

 been defined as ''discontinuous growth"; thus the 

 growth of a plant-cutting is a reproduction, and many 

 cases of asexual reproduction in animals illustrate the 

 same phenomenon (reproduction by fission, regeneration). 

 In the lowest organisms, e.g., bacteria, it becomes no 

 longer a matter of practical interest to distinguish 

 between growth and reproduction. Heredity, the re- 

 semblance of offspring or outgrowth to parent stock, is 

 illustrated in all of these cases; the special problem of 

 heredity, therefore, is reducible ultimately to the funda- 

 mental problem of the conditions determining the 

 property of specific construction possessed by all forms 



^ Cf. the discussion by Child, Senescence and Rejuvenescence, Chicago 

 (1915), chap. ii. 



