Vol. XXXVI. April, IQIQ. No. 4 



BIOLOGICAL BULLETIN 



PRECIPITATION-STRUCTURES SIMULATING OR- 

 GANIC GROWTH. II. 



A CONTRIBUTION TO THE PHYSICO-CHEMICAL ANALYSIS OF 



GROWTH AND HEREDITY. 



RALPH S. LILLIE AND EARL N. JOHNSTON, 

 FROM THE LABORATORY OF GENERAL PHYSIOLOGY, CLARK UNIVERSITY 



PART I. THEORETICAL. 



The problem of growth, reduced to its simplest terms, is the 

 problem of the conditions under which structure of a definite 

 and specific kind is built up by the growing system through the 

 chemical and physical transformation of material taken from 

 the surroundings. As thus expressed, our definition applies to 

 inorganic as well as to organic growth, e. g., to the formation of a 

 crystal from its "mother-liquid," or of a metallic deposit at a 

 cathode. Both of these processes, especially the latter, exhibit 

 many significant analogies to organic growth-processes; thus a 

 crystalline or electrolytic deposit of a given chemical composition, 

 laid down under constant external conditions, has, like an organic 

 growth, its own definite and specific structural peculiarities. In 

 organic growth and development, however, numerous complexities 

 enter which are absent from inorganic growth; in particular the 

 continual chemical and physical activity of the living system is 

 always present as a dominating factor; this activity is itself 

 specific and modifies in a specific manner the structure-forming 

 processes, and is itself modified by them. Since every living 

 organism is by its very nature an active system of this kind, the 

 problem of organic growth becomes one relating not merely to 

 the origination of specific structure but of specific physiological 

 processes and activities as well, some of which are demonstrably 

 dependent upon the observed structure, while others are related 



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