THE UNIQUENESS OF THE INDIVIDUAL 



no less than ten times its original area. The number of hair 

 roots is not added to,^ so that the most obvious outward 

 evidence of intercalary growth is the fact that the hairs growing 

 from the central island become spaced apart to a degree pro- 

 portional to its linear enlargement. There is nothing particu- 

 larly novel or mysterious about the intercalary enlargement of 

 skin, for it is a process that occurs naturally in growth from 

 newborn to adult size. It is made particularly obvious by the 

 fact that when a child is grafted with skin, the graft grows 

 with him. 



Contracture and intercalary expansion between them make 

 for admirably efficient healing in rabbits. Why do they not 

 work to equally good effect in men? 



The answer is probably anatomical. Contracture can only 

 be an efficient healing process if the skin is sufficiently loose to 

 '■give'' while it is going on. In rabbits, and in mammals generally, 

 the integument is very loosely knit to the body wall; its main 

 blood supply runs in a plane parallel to the surface, and it 

 contains its own intrinsic musculature (the ""panniculus 

 carnosus"") which makes it possible for mammals to twitch their 

 skins. In human beings, the integument is no longer a gener- 

 ously fitting coat, but is much more firmly knit to the tissues 

 below; the intrinsic muscles of the skin are now confined to 

 areas of the face and neck, and the skin generally is much more 

 of a piece with the rest of the body. The upshot of this new 

 anatomical arrangement is that contracture, so far from being 

 an efficient mechanism of wound closure, has become something 

 of a menace; it constricts, disfigures and distorts, and may yet 

 fail to bring the edges of the wound together. But it still occurs: 



^ Dr Breedis has recently shown tliat, contrary to almost all expert belief, 

 the number of hair roots can be added to in adult animals, and my col- 

 leagues R. E. Billingham and Paul Russell have done experiments which 

 entirely bear out his views. The new formation of hair roots, however, takes 

 place only under certain special circumstances that do not affect experi- 

 ments of the kind described above. 



132 



