THE IMPERFECTIONS OF MAN 



donor area will therefore heal of its own accord without scar- 

 ring or contraction.) 



The question is, why is the rabbit so accomplished in wound 

 healing and the human being so strikingly inept; the answer 

 turns upon an understanding of the mechanism of healing as 

 it occurs in a rabbifs skin. 



As Billingham and I see it, there are two quite distinct 

 (though concurrent) elements in the healing of rabbits'* skin. 

 The first is contracture, which closes the wound by a progres- 

 sive coming together of its original edges. Contracture follows 

 a regular geometric pattern: starting as a rectangle, the wound 

 first becomes smaller wdthout changing shape; then the sides 

 cave in towards the centre, and meet from the four corners 

 inwards, so that all that is left is a neat )> — <^ shaped line of 

 suture (it does not deserve to be called a scar). During the 

 process of contraction the raw wound area is temporarily 

 covered by a thin film of skin epithelial cells which grow or 

 migrate inwards from the edges of the wound; but as the 

 original skin edges come together, so the space enclosed by 

 them diminishes and finally disappears, and the skin epithelium, 

 which is purely a temporary organ of healing, disappears 

 with it. 



Contracture closes the wound, but it does not, of course, 

 make good the loss of 100 cm.^ of skin. Billingham and I believe 

 that this loss is made good by a second process, the intercalary 

 or ''intussusceptive^ growth of the remaining skin. Intercalary 

 growth is an expansion of the skin by growth on or within its 

 existing fibrous framework. The simplest way of demonstrat- 

 ing it is to prepare a rectangular wound and to leave behind, 

 in its centre, a small area of undamaged skin. Alternatively, 

 skin may be excised from the whole of the area and a skin graft 

 thereupon placed in the middle. The forces of contracture 

 which draw the skin edges together bring an expansive force to 

 bear on the central island, which may accordingly enlarge to 



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