PIGMENT CELLS. 259 



and bronchial glands of aged persons and animals has been 

 the subject of much discussion ; nor has it been as yet de- 

 cided whether it be true pigment, or merely a deposition of 

 carbon. Pearson * maintained the opinion that the colouring 

 matter is the powder of carbon, since neither chlorine nor the 

 mineral acids act upon it. 



In those remarkable luces natures, Albinoes, there would 

 appear to be an absence of pigmentary granules in all parts 

 of the body, even in the eye : the pigment cells themselves 

 are stated to exist, but to be wanting in their characteristic 

 coloured contents. 



Pigment cells do not present the same size, form, and cha- 

 racter wherever they are encountered. 



Thus those of the choroid are adherent, large, flattened, 

 polygonal, mostly hexagonal, with clear nuclei and margins ; 

 occasionally, however, it happens that both nuclei and cell 

 wall are obscured by the number and disposition of the con- 

 tained granules : the cells are mostly of uniform size as well 

 as shape, in consequence of which regularity they form a 

 very beautiful microscopic object ; sometimes, however, one 

 cell is observed to be larger than the rest, octagonal, and 

 surrounded by a number of cells of smaller size than ordinary, 

 and mostly pentagonal. 



According to Henle f , the contained granules are situated 

 in the posterior part of each cell, while the nucleus is placed 

 in its anterior division ; it is this arrangement which allows 

 of the nucleus being so clearly seen ; in those cases, however, 

 in which the nucleus is obscured, acetic acid will frequently 

 bring it into view ; this, if concentrated, will dissolve the cell 

 wall, set free the granules, and leave the nucleus. 



Schwann states that he has seen the pigmentary granules 

 in the cells of the choroid in active motion. 



The cells of the choroid form by their adherence a mem- 

 brane resembling the most regular and beautiful mosaic 

 pavement in miniature. 



* Philosophical Transactions, 1813, pi. ii. p. 159. 

 | Anat. Gen. vol. vi. p. 295. 



