CHAPTER I. 



THE ENLARGEMENT OF PARTS FROM INCREASED USE, 

 OVERGROWTH, AND IRRITATION. 



IT is well established that the increased use of a part 

 tends to enlarge and strengthen it, that disuse on the other 

 hand often leads to its diminution and enfeeblement : 

 structural modifications thus induced are inherited. 



The truth of the first part of this statement may be 

 demonstrated by a simple experiment : Let the arm of a 

 healthy person be firmly strapped for several consecutive 

 days upon a splint in a few days the muscles will be 

 softer than usual and actual measurements will show 

 that the limb has diminished in size. Allow the arm to 

 resume its function ; the lost ground will be quickly 

 recovered. 



When a young and vigorous person has the mis- 

 fortune to lose an arm the remaining limb, being used 

 for all purposes, will rapidly increase in size and strength. 

 The same facts may be observed in dogs and cats which 

 have lost a limb or part of a limb. A woman, aged fifty, 

 had her big toe, including the metatarsal bone, ampu- 

 tated ; six months after she had regained the use of the 

 foot, the second toe had enlarged, and stood out from its 

 fellows in such a way as to' resemble in size and general 

 appearance the lost toe indeed, when the foot was 



