L9i 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 withdrav7 



