600 Mr. Charles Merrier [May 3, 



succulent sprout, the soft immature claw, is more easily injured than 

 its original. That is to say, when once it has heen mutilated, when 

 once it has heen distorted, when once it Las received a set, subsequent 

 alteration in the same sense is facilitated. 



Again, when the mutilation is repeated, subsequent reproduction 

 is less vigorous ; and if the mutilation is repeated sufficiently often, 

 reproduction fails. The temporary set becomes, alter sufficient repe- 

 tition, a permanent set. 



Similarly, when the higher animals are wounded, there is at first 

 a pause, and then the process of repair sets in, with a speed which 

 for a short time increases, and then gradually slackens, until the 

 latest stages, the devascularisation of the scar, and its assimilation 

 to adjoining tissues, become imperceptibly slow. Moreover, in pro- 

 portion to the immaturity of the healing process is the vulnerability 

 of the wound. It is more easily injured again than are uninjured 

 parts. The set that has been impressed upon it facilitates a further 

 set in the same direction. Furthermore, if the wound is opened 

 again and again, or is not suffered to close, the healing process at 

 length fails ; the temporary set becomes a true permanent set. 



"When the old physicians spoke of the vis medicatrix naturae, they 

 did but express in other words the tendency of a set to disappear, the 

 transiency of a distortion ; and when the physicians of a later day 

 insist upon the frequency with which acute change supervenes upon 

 chronic, they do but state in different terms the existence of that 

 dynamic memory which facilitates a further change in the same 

 direction as a previous change. 



It would scarcely be too fanciful a view to regard the succession 

 of organisms in a race, as a continuous body, subject to the influence 

 of distorting agents. Such a distortion takes place when a race of 

 animals or plants is subjected to new conditions of life — for instance, 

 when a wild animal is domesticated, or a wild plant brought into 

 cultivation. In such a case the whole structure of the organism is 

 profoundly modified. As long as the distorting agent acts, as long 

 as the domestication continues, so long continues the distortion. But 

 let individuals of the domesticated race escape and breed in wildness, 

 and after a time they will begin to revert, both in themselves and in 

 their offspring, to the feral type ; and this change will take place at 

 first with increasing, and subsequently with diminishing speed. The 

 race has received a temporary set, a structural memory of its expe- 

 riences in the faimyard, the garden or the greenhouse, a set which 

 diminishes when the distorting agent ceases to act. If we wish to 

 modify the form of an organism, we shall more easily succeed by 

 choosing for our experiment one that has already undergone recent 

 modification than one of fixed type, for practical breeders know, 

 although they express their knowledge in other words, that a set 

 once produced facilitates further change in the same direction. 



It does not seem unjustifiable to infer that what is true of these 

 gross and sensible distortions is true also of the delicate and infini- 



