484 PROCESSES INFERRED FROM INDIRECT OBSERVATION 



which is again of the monomolecular form, save that the constant "a" 

 in the formula is no longer proportional to the actual concentration 

 of the substrates, but to the nth power of their concentration. That 

 the backward reaction should be monomolecular is, of course, not a 

 matter for surprise, since we may suppose that the majority of decom- 

 positions which living tissue suffers consists in the interaction of a single 

 molecule of some protoplasmic constituent either with water or with 

 oxygen, the concentration of both of which substances is maintained 

 automatically at an approximately constant level in the tissues. 



Thus the synthesis of a protein involves the interaction of many 

 different amino-acid molecules, but its hydrolysis in dilute aqueous 

 solution obeys the monomolecular formula, because only a single species 

 of molecule, that of the protein itself, is undergoing appreciable change 

 of mass or concentration in the process. 



Summarizing the general characteristics of the growth-process we 

 may therefore state : 



1. That the growth of man and of animals takes place in periods or 

 cycles in which slow and rapid growth alternate, three of the cycles 

 being usually appreciable in magnitude. 



2. Each of the growth-cycles is the expression of an underlying self- 

 accelerated chemical process. 



3. The accelerating factor is some substance or group of substances 

 produced during growth. 



4. The supply of nutriment capable of transformation into living 

 tissues may, in normal animals, be regarded as constant and undimin- 

 ished by the process of growth itself. 



5. The inhibiting factor, which ultimately brings the growth in any 

 given cycle to a standstill, is the accumulation of the products of growth. 



6. Removal of these products, as by local death or injury, or by 

 general inanition, reinaugurates the process of growth, which continues 

 until equilibrium is reattained. 



7. The whole of the diverse processes which in the aggregate con- 

 stitute growth are governed and determined in rate and magnitude by 

 the specificially slowest essential process. 



8. The forward reaction in the governing process may involve the 

 interaction of many different molecules, but the reverse reaction 

 appears, in many cases at least, to involve the decomposition of only 

 a single species of molecule of variable mass or concentration. 



THE INFLUENCE OF RACE, SEX, AND ENVIRONMENT UPON 

 THE GROWTH-PROCESS. 



The fact that the bodily dimensions of a given species of animal 

 never exceed certain characteristic upper limits, no matter how favor- 

 able the environmental conditions may be with respect to the abun- 

 dance and variety of Nutrients, shows that the factors which inhibit the 



