THE MICROSCOPE IN PHYSIOLOGY. 95 



are black ; in white races they are pink. It is clear 

 that these pigment cells are confined to the cuticle 

 and Malpighian stratum alone ; for the cutis vera of 

 a negro is as pink as that of the fairer races, so that 

 the colour is not even " skin deep/' The subject of 

 epidermic pigment-cells has always appeared to me to 

 be full of deep and curious interest. How are these 

 pigment-cells affected ? Why are they black in the 

 negro, olive in the Mongolian, copper-coloured in the 

 North American, pink in the Saxon ? Why are they 

 altogether absent in the Malpighian layer of albinoes ? 

 The sun would appear to have the power of darkening 

 the pigment-cells, for the exposed parts of a negro 

 are blacker than those which are unexposed. The 

 Jews, moreover, who settled centuries ago in India, 

 "have become as dark as the Hindoos around them." 

 But even in the same individual these epidermic pig- 

 ment-cells are subject to change. " Can the Ethiopian 

 change his skin ? " asks the Hebrew prophet. Cases 

 of such change of colour have occasionally occurred. 

 " One case is that of a negro slave in Kentucky, aged 

 forty-five, who was born of black parents, and was 

 himself perfectly black until twelve years of age. At 

 that time a portion of the skin, an inch wide, encircling 

 the cranium, just within the edge of the hair, gradually 

 changed to white, also the hair occupying that locality. 

 A white spot next appeared near the inner canthus of 

 the left eye ; and from this the white colour gradually 

 extended over the face, trunk, and extremities, until 

 it covered the entire surface. The complete change 

 from black to white occupied about ten years ; and 

 but for the hair, which was crisped or woolly, no one 

 would have supposed at this time that his progenitors 

 had offered any of the characteristics of the negro, 

 his skin presenting the healthy vascular appearance of 

 that of a fair-complexioned European. When he was 



