CKAP. XIV.] STRUCTURE OF THE CUTICLE. 



413 



as the soles of the feet and the palms of the hands. In the 

 same parts, too, it varies with the amount of pressure to which 

 it is subjected at different times; whence F ig. ss, 



the hard hands of the artizan, compared 

 with those of persons who have spent 

 their time in gentler occupations. This 

 increase in thickness probably results from 

 the mechanical stimulus applied to the 

 capillaries of the part. But, in whatever 

 manner it may admit of explanation, there 

 is scarcely a more striking instance of that 

 inherent power which the body possesses 

 of adapting itself to varied external cir- 

 cumstances, than this one presented by 

 the human cuticle. 



This investment is not permeated by 

 either vessels or nerves, but consists solely 

 of a congeries of nucleated particles, ar- 

 ranged in numerous superimposed laminae, 

 and united together by an intervening 

 substance in very small quantity. Those 

 particles that lie deepest, and rest imme- 

 diately on the cutis, are little more than 

 small granules, scattered in a homogeneous 

 matrix, which serves to unite them to- 

 gether. Those of the next layers are 

 rounded cells, consisting of a transparent 

 membrane, in which similar granules, but 

 somewhat larger in size, are visible. In 

 the succeeding layers these cells are more 

 and more compressed as they are nearer 

 to the surface; and on the surface they 

 are so flattened, that their opposite sur- 

 faces are in contact, and adhere, forming 

 mere scales, in which the nucleus remains. 

 The diameter of the deep particles is about 

 3-oVo inch, and of the superficial ones ^ 

 inch. 



We know that the superficial scales are being continually shed 

 in small lamelliform masses, and it is evident that their loss is 

 supplied from below ; hence new particles must be constantly pro- 

 duced in the deepest layers, and must be in uninterrupted advance, 



Vertical section of the sole: . 



