CHAP. XIV.] COLOURING MATTER OF THE SKIN. 415 



These facts will go far to explain why it happens that the union 

 between the particles composing the same layer is in general more 

 intimate than that between different layers, so that it is not difficult 

 to divide the cuticle into two, three, or more laminae : and, in par- 

 ticular, why it is easy, at a certain stage of maceration, to separate 

 the harder from the softer layers, and thus to isolate the structure 

 termed " rete Malpighii." This is nothing more than the deepest, 

 or most recently formed, part of the cuticle. When isolated, it 

 presents depressions, or sometimes complete apertures, which have 

 been occupied by the projecting papillae ; and hence the term rete. 

 When apertures exist, the cuticle on the top of the papillae has 

 been detached with the outer hard layer, and that in contact with 

 and encircling their bases remains by itself. 



In the coloured races of mankind, there is, at first sight, some 

 ground for supposing the rete Malpighii to be a structure distinct 

 from the other layers of the cuticle, the colouring matter being 

 found to reside chiefly in this part. However various in quantity 

 and hue, the colouring matter always consists of oblong or oval 

 grains of extreme minuteness ( 2 - \ of an inch in their long 

 diameter), and occupying the interior of some of the epidermic 

 particles. In the negro it is accumu- Fig 85 



lated in enormous quantity, and com- 

 pletely envelops the nuclei itnmedi- f= 

 ately resting on the cutis. On exa- 

 mining a vertical section of the whole 

 cuticle, we find the colouring matter 

 gradually diminishing as we approach 



flip nvfir>P 5rr1 if ic mncf nlfar> tlinf Vertical section of the cnticle, from the 

 ^ SU1 lace , ana It IS mOSt Cieai mat scro tum of a negro, a. Deep cells, 



la Tin triiP linP nf rlpmnrpnfinn loaded with Pigment. b. Cells at a 

 demarcation h i g i ier i eve i, pa ler, and more flattened. 

 lio ftirrk -tfir-na Wo matr e. Cells at the surface, scaly and colour - 



he two portions, w e may less> as in the white rac es. Magnified 

 observe the colour of the rete mucosum 30 diameters - 

 deeper at points; and a greater proportionate depth of colour 

 is traceable over such points, through all the layers, as far as 

 the surface : we may even discern a sort of stream of coloured 

 grains advancing towards the surface. Hence there can be little 

 doubt that the decrease of colour in the superficial laminae is due 

 to that chemical change which has just been described as gra- 

 dually taking place in the interior of the epidermic particles. As it 

 is not always easy in this country to obtain specimens of the negro's 

 skin, the above facts may be verified in the skin of coloured domes- 

 tic animals, or, less satisfactorily, in that of some portions of the 

 skin of the white race, as that of the scrotum, of the nipple during 



