19 i THE INDUCTIONS OF BIOLOGY. 



essentially like re-action of functions on structures. From tLe 

 laws of adaptive modification in societies, we may therefore 

 hope to get a clue to the laws of adaptive modification in 

 organisms. Let us suppose, then, that a society has arrived 

 at a state of equilibrium like that of a mature animal — a 

 state not like our own, in which growth and structural de- 

 velopment are rapidly going on ; but a state of settled 

 balance among the functional powers of the various classes 

 and industrial bodies, and a consequent fixity in the relative 

 sizes of such classes and bodies. Further, let us suppose 

 that in a society thus balanced, there occurs something which 

 throws an unusual demand on some one industry — say an 

 unusual demand for ships (which we will assume to be built 

 of iron) in consequence of a competing mercantile nation 

 having been prostrated by famine or pestilence. The imme- 

 diate result of this additional demand for iron ships, is the 

 employment of more workmen, and the purchase of more iron, 

 by the ship-builders ; and when, presently, the demand con- 

 tinuing, the builders find their premises and machinery in- 

 sufficient, they enlarge them. If the extra requirement 

 persists, the high interest and high wages bring such extra 

 capital and labour into the business, as are needed for new 

 ship-building establishments. But such extra capital and 

 labour do not come quickly ; since, in a balanced community, 

 not increasing in population and wealth, labour and capital 

 have to be drawn from other industries, where they are 

 already yielding the ordinary returns. Let us now go a 

 step further. Suppose that this iron-ship-building industry, 

 having enlarged as much as the available capital and labour 

 permit, is still unequal to the demand ; what limits its im- 

 mediate further growth ? The lack of iron. By the hypo- 

 thesis, the iron-producing industry, like all the other indus- 

 tries throughout the community, yields only as much iron as 

 is habitually required for all the purposes to which iron is 

 applied : ship-building being only one. If, then, extra iron 

 is required for ship-building, the first effect is to withdraw 



