62 PIGMENTATION. 



the cells ; moreover, the granular varlety^ of pigment — which, 

 we may remark by the way, is much the more usual form, 

 crystals of ha^matoidiu ranking among curiosities — is equally 

 abundant within and around the cells. It consists, as the name 

 shows, of minute yellow, brown, or black (melanin) granules, 

 collected into little groups, which may unite under certain condi- 

 tions to form larger masses of a more homogeneous character. 

 Should they be numerous enough to fill the protoplasm of a cell, 

 the colourless nucleus is partly pushed aside, partly surrounded ; 

 the pigmented cell appearing to be perforated by a circular gap 

 or hole. Flat cells (choroid coat of the eye), in which the 

 nucleus is in contact with both surfaces at once, retain their 

 characteristic aspect. In spheroidal cells, however, the nucleus 

 ultimately disappears, leaving a coloured corpuscle, in which 

 only the external form of the cell can still be recognised. 



§ 59. It is very unlikely that the functions of the cells are 

 much impaired by pigmentary infiltration, for we find partial 

 infiltrations of this nature in many of the most vitally important 

 elements of the organism. I refer particularly to certain groups 

 of motor ganglion-cells in the crura cerebri, whose constant im- 

 pregnation with pigment has led to that region being designated 

 as substantia nigra vel ferruginea. In the majority of local pig- 

 mentations, however, this question admits of no solution ; for 

 we cannot distinguish the functional troubles due to pigmentary 

 infiltration from those which may have resulted from the ante- 

 cedent local disorder. The opportunities affbrded by certain 

 pigmentary infiltrations originating in dyscrasia? are much more 

 favourable for this inquiry. I do not refer to melancemia, which 

 only deserves the name of a dyscrasia, inasmuch as a black pig- 

 ment of local origin (in the spleen), enters the blood, and remains 

 an abnormal constituent of this fluid during a certain time. 

 When the deposit of this pigment in the capillaries of the brain 

 gives rise to serious functional disturbances, these differ in 

 no respect from such as might be produced by plugging of these 

 vessels from any cause whatever; they cannot, therefore, be 

 ascribed to the pigment as such. So too, the quantitative excess 

 of colour in the skin, which Addison ascribes to a disease of the 

 supra-renal bodies, is ill-adapted for our present purpose, owing 

 to the obscurity which still hangs over the entire process. On 

 the other hand, the history of melanotic sarcoma {see Morbid 



