HEREDITY FROM PHYSICO-CHEMICAL POINT OF VIEW. 83 



activity predominates, a similar dependence of formative activity 

 on function must exist. This is the kind of relation emphasized 

 recently by Child, when he describes the developing organism 

 not as being first constructed and then functioning, after the 

 manner of a machine, but as constructing itself by functioning. 1 

 Growth and development are peculiar in that specific construc- 

 tion overbalances destruction, and that the synthesized material, 

 as it accumulates, adopts a definite organization. But this 

 accumulation of structure is itself the expression or result of 

 active functioning, in which energy is freed, just as growth is 

 such an expression in a muscle which has been exercised. Ap- 

 parently we must conclude that part of this energy is expended 

 in the work of synthesizing and arranging the specific structural 

 material of the organism or cell. We have already seen that this 

 specific material consists essentially of protein. We are thus 

 brought back to the question: what are the conditions under 

 which protein is synthesized in the living cell and deposited as 

 structure? 



No very definite or certain answer can be given at present to 

 this question. But we seem to be in a position to rule out certain 

 possibilities, and perhaps to affirm others. First we must note 

 more particularly the significance of the long recognized fact 

 that many vital syntheses require the addition of energy to the 

 synthesized compounds; this is seen, for instance, in the forma- 

 tion of fats from proteins and carbohydrates. Now since such 

 syntheses, where compounds of higher chemical potential are 

 built up from those of lower, take place continually in all cells, 

 it appears highly probable that their conditions are also the main 

 conditions of synthesis in general, and that a subordinate impor- 

 tance is to be attached to the purely enzymatic type of synthesis. 

 Both experience and theory show that the latter is limited to 

 the formation of compounds in which little change of energy 

 'accompanies the transformation; 2 hence it is plainly insufficient 

 to meet the normal requirements of constructive metabolism. 

 Some kind of mechanism would seem to be indicated in which 

 energy derived from oxidation or other chemical source is applied 



1 C. M. Child, "Individuality in Organisms." University of Chicago Press, 

 1915, p. 16. 



2 Cf. Hober's " Physikalische Chemie der Zelle und dcr Gewcbe," 1914, p. 677. 



