ADAPTATION. 191 



duced by antagonist organic actions, cannot any of them be 

 carried to an excess in one direction, without there being 

 produced an equivalent excess in the opposite direction. It 

 is a corollary from the persistence of force, that any deviation 

 effected by a disturbing cause, acting on some member of a 

 moving equilibrium, must (unless it altogether destroys the 

 moving equilibrium) be eventually followed by a compensating 

 deviation. Hence, that excess of repair should succeed ex- 

 cess of waste, is to be expected. But how happens the mean 

 state of the organ to be changed ? If daily extra waste 

 naturally brings about daily extra repair, only to an equiva- 

 lent extent, the mean state of the organ should remain con- 

 stant. How then comes the organ to augment in size and 

 power ? 



Such answer to this question as we may hope to find, must 

 be looked for in the effects wrought on the organism as a 

 whole, by increased function in one of its parts. For since 

 the discharge of its function by any part, is possible only on 

 condition that those various other functions on which its own 

 is immediately dependent, are also discharged ; it follows 

 that excess in its function presupposes some excess in their 

 functions. Additional work given to a muscle, implies ad- 

 ditional work given to the branch arteries which bring it 

 blood, and additional work, smaller in proportion, to the 

 arteries from which these branch arteries come. Similarly, 

 the smaller and larger veins which take away the blood, aa 

 well as the absorbents which carry off effete products, must 

 have more to do. And yet further, on the nervous centres 

 which excite the muscle, a certain extra duty must fall. But 

 excess of waste will entail excess of repair, in these parts as 

 well as in the muscle. The several appliances by which the 

 nutrition and excitation of an organ are carried on, must also 

 be influenced by this rhythm of action and re-action ; and 

 therefore, after losing more than usual by the destructive 

 process, they must gain more than usual by the constructive 

 process. But temporarily-increased efficiency in these ap- 



