258 THE SOLIDS. 



white race, and the colouring matter of the granules is doubt- 

 less also darker. 



In the white, however, a greater or less number of pig- 

 ment cells is almost invariably found in certain situations, as 

 in the eye, on the internal surface of the choroid, and the 

 posterior aspect of the iris and ciliary processes, also between 

 the sclerotic and choroid; in the skin at certain localities 

 where it is placed beneath the dermis and epidermis, as in 

 the areola round the nipples, especially of women, and about 

 the perinaeum and genital organs. 



In the black races, pigment cells follow a similar distribu- 

 tion in the eye ; but beneath the epidermis, as also under the 

 nails, they form a continuous stratum composed of super- 

 imposed layers of cells. 



There are yet other situations in which pigment cells have 

 been encountered : thus Valentin * has signalised the occur- 

 rence of pigmentary ramifications in the cervical portion of 

 the pia mater, to which they impart a blackness perceptible 

 to the unaided sight. 



Again, Wharton Jones f has described a thin but evident 

 layer of brown pigment in the membranous labyrinth of the 

 ear of man. It has been observed in other mammalia in 

 which it is still more marked, in the same situation, by 

 Scarpa, Comparetti, and Breschet.J 



The brown spots, known by the name of freckles, with 

 which the faces of most persons are more or less covered in 

 summer, are due to a development of pigment cells. 



A development of pigmentary matter frequently takes 

 place as the consequence of disease ; thus, it is of common 

 occurrence to meet with growths either entirely or in part 

 composed of pigment cells, the tumours, with the proper 

 structure of which it usually thus intermingled, being those 

 of cancer or medullary fungus. 



The nature of the pigment-like matter found in the lungs 



* Verlauf und Enden der N erven, p. 43. 



f Article HEARING in the Cyclopaedia of Anatomy and Physiology, t. ii. 

 p. 529. 



J Recherches sur 1'Organe de 1'Ou'ie de THomme, Paris, 1836, in 4to. 



