LONG PERSISTING ADJUSTMENTS 175 



doubt there is always some lasting impression, for even the bar 

 of iron is never quite the same after it has been once struck ; 

 but the results of the slight organic changes we have been 

 alluding to are usually lost as the sand-ripples are lost when 

 the tide turns. They are the merely transient results of re- 

 sponses to frequently recurring environmental changes to which 

 the organism is well accustomed. 



3. Adjustments which persist for a Considerable Time. 

 Insensibly, however for it is all a matter of degree we pass 

 from transient results to others which last for a considerable 

 time. We are browned by the sun on our summer holiday, and 

 the result may last far into the autumn. The change, though 

 still very superficial, has taken a firmer hold. The world is 

 full of illustrations the increase in the child's weight after 

 a month at the farm, the increase in the size of the muscles after 

 a course of Sandow exercises, the warping of the plant-stem 

 which has been illumined from one side only, the blanching of 

 the banked-up celery. But these results do not last long after 

 the inducing conditions have ceased to operate. Sooner or 

 later there is a return to the normal. Like a bow unstrung, 

 the organism rebounds approximately to its previous state. 

 The stimulus ceases or the absent stimulus is restored, and 

 the organism, as if at the command "As you were," returns 

 to the status quo. 



4. Modifications. Insensibly, however for it is still only a 

 matter of degree we pass from these temporary changes to 

 others which are demonstrably permanent. For there are cases 

 where the new stimulus provokes a structural change, which 

 persists after the stimulus has ceased. As we have put it, 

 metaphorically, the limit of organic elasticity has been trans- 

 cended. These are what in technical language we call " acquired 

 characters " or " modifications." 



The Englishman who works half his lifetime under a tropical 

 sun may become so tanned that the result does not disappear 



