196 THE INDUCTIONS OF BIOLOGY. 



and labour from other investments and occupations. And 

 until the permanent extra demand for coal, has become great 

 enough to draw from other investments and occupations, suf- 

 ficient capital and labour to sink new mines, the increasing 

 production of iron must be restricted by the scarcity of coal ; 

 and the multiplication of ship-yards and ship-builders, 

 must be checked by the want of iron. Thus, in a com- 

 munity which has reached a state of moving equilibrium, 

 though any one industry directly affected by an additional 

 demand, may rapidly undergo a small extra growth ; 

 yet a growth beyond this, requiring, as it does, the build- 

 ing-up of subservient industries, less directly and strongly 

 affected, as well as the partial e^building of other industries, 

 can take place only with comparative slowness. And a 

 still further growth, requiring structural modifications of 

 industries still more distantly affected, must take place still 

 more slowly. 



Returning from this analogy, we realize more clearly the 

 truth, that any considerable member of an animal organism, 

 cannot be greatly enlarged without some general re-organiza- 

 tion. Besides a building-up of the primary, secondary, and 

 tertiary groups of subservient parts, there must be an un- 

 building of sundry non-subservient parts ; — or at any rate, 

 there must be permanently established, a lower nutrition of 

 such non- subservient parts. For it must be remembered that 

 in a mature animal, or one which has reached a balance 

 between assimilation and expenditure, there cannot be an in- 

 crease in the nutrition of some organs, without a decrease in 

 the nutrition of others ; and an organic establishment of the 

 increase, implies an organic establishment of the decrease — 

 implies more or less change in the processes and structures 

 throughout the entire system. And here, in- 



deed, is disclosed one reason why growing animals under- 

 go adaptations so much more readily than adult ones. For 

 while there is surplus nutrition, it is possible for specially- ex- 

 ercised parts to be specially enlarged, without any positive 



