ADAPTATION. 193 



specially- exercised organ, a considerable extra power must 

 be gained by a series of immediately- subservient organs, and 

 some extra power by a secondary series of remotely-sub- 

 servient organs. Thus there are required numerous and 

 wide-spread modifications. Before the artery which feeds a 

 hard-worked muscle, can permanently furnish a large ad- 

 ditional quantity of blood, it must increase in diameter and 

 contractile power ; and that its increase of diameter and con- 

 tractile power may be of use, the main artery from which it 

 diverges, must also be so far modified as to bring this addi- 

 tional quantity of blood to the branch artery. Similarly 

 with the veins ; similarly with the absorbents ; similarly 

 with the nerves. And when we ask what these subsidiary 

 changes imply, we are forced to conclude that there must be 

 an analogous group of more numerous changes, ramifying 

 throughout the system. The growth of the arteries prima- 

 rily and secondarily implicated, cannot go to any extent, 

 without growth in the minor blood-vessels on which their 

 nutrition depends ; while their greater contractile power in- 

 volves enlargement of the nerves which excite them, and 

 some modification of that part of the spinal cord whence 

 these nerves proceed. Thus, without tracing the like remote 

 alterations implied by extra growth of the veins, absorbents, 

 and other agencies, it is manifest that a large amount of re- 

 building must be done throughout the organism, before any 

 organ of importance can be permanently increased in size 

 and power to a great extent. Hence, though such extra 

 growth in any part as does not necessitate considerable 

 changes throughout the rest of the organism, may rapidlv 

 take place ; a further growth in this part, requiring a re- 

 modelling of numerous parts remotely and slightly affected, 

 must take place but slowly. 



We have before found our conceptions of vital processes 

 made clearer by studying analogous social processes. In 

 societies there is a mutual dependence of functions, essentially 

 like that which exists in organisms; and there is also an 



