192 THE INDUCTIONS OF BIOLOOY. 



pliances by which, blood and nervous force are brought to an 

 organ, will cause extra assimilation in the organ, beyond 

 that required to balance its extra expenditure. Regarding 

 the functions as constituting a moving equilibrium, we may 

 say, that divergence of any function in the direction of in- 

 crease, causes the functions with which it is bound up to 

 diverge in the same direction ; that these again cause the 

 functions which they are bound up with, also to diverge in 

 the same direction ; and that these divergences of the con- 

 nected functions, allow the specially- affected function to be 

 carried further in this direction than it could otherwise be 

 — further than the perturbing force could carry it if it had a 

 fixed basis. 



It must be admitted that this is but a vague explanation. 

 Among actions so involved as these, we can scarcely expect 

 to do more than dimly discern a harmony with first princi- 

 ples. That the facts are to be interpreted in some such way, 

 may, however, be inferred from the circumstance that an 

 extra supply of blood continues for some time to be sent to 

 an organ that has been unusually exercised ; and that when 

 unusual exercise is long continued, a permanent increase of 

 vascularity results. 



§ 69. Answers to the questions — Why do these adaptive 

 modifications in an individual animal, soon reach a limit? 

 and why, in the descendants of such animal, similarly condi- 

 tioned, is this limit very slowly extended ? — are to be found 

 in the same direction as was the answer to the last question. 

 And here the connexion of cause and consequence is much 

 more manifest. 



Since the function of any organ is dependent on the func- 

 tions of the organs which supply it with materials and forces ; 

 and since the functions of these subsidiary organs are de- 

 pendent on the functions of organs which supply them with 

 materials and forces ; it follows that before any great extra 

 power of discharging its function, can be gained by a 



