132 SIMPLE HISTOLOGICAL ELEMENTS. 



give the gray color to the cells of the cortical substance of the 

 cerebrum and cerebellum, and the central part of each half of the 

 spinal cord ; and pigment-cells are also found in the cervical pia 

 mater and the membranous labyrinth. 



In negroes, the skin also contains a layer of pigment-cells over 

 the whole surface of the body; and to this its blackness is due. 

 This is the last formed and deepest layer, consisting of cells lying 

 directly on the basement membrane of the skin. Similar cells, 

 darker than the rest, also exist in this layer of the skin of Eu- 

 ropeans, but their pigment is of a lighter color. In fact, the differ- 

 ence in amount and color of pigment 

 Flg ' 68> in this layer of cells gives rise to all 



the varieties of color presented by the 

 different races of men. Fig. 68 repre- 

 sents the appearance of the several 

 layers of cells in the cuticle of the 



Section of the cuticle of the negro. ne j n the Quter l ayers w bich are 



a. Deep cells, loaded with pigment, b. S ' 



< Cells at a higher level, paler and more flattened into SCaleS, the pigment is 



flattened c Cells at the surface, scaly tird aDS ent. If the Cuticle of the 



and colorless, as in the white races. J 



negro be removed by a blister, the 



pigment-cells on its inner surface will be found clustered together 

 around circular spots of a bright color where the cells are wanting. 

 'The spots correspond to the depressions in the under surface of the 

 cuticle into which the papillae of the skin projected. On the other 

 hand, in albinoes 1 no pigment-granules are found in the epidermis 

 at all. 



Freckles upon the skin of the white races, whether congenital or 

 otherwise, are also due to a development of pigment cells in the 

 layer next underneath the epidermis the Malpighian stratum. 



The pigment in the lungs of man and the lower animals, both 

 under the pleura and in the parenchyma, is in the form of granules; 

 but which are not contained within cells. They are probably mere 

 particles of carbon. In the lower animals, a single lobe is some- 

 times quite black, while the rest remains unchanged; though a 

 section of it shows that its function is not essentially, if at all, im- 

 paired by the deposit. 



1 So called from albus, white. 



