PIGMENT CELLS. 257 



ART. XII. PIGMENT CELLS. 



Colouring matter is found in the animal organisation in 

 two states, either diffused throughout the fluid contents of 

 colourless cells, as in fat cells generally, but especially in 

 those of the iris of birds, and as in the liver cells, and red 

 blood discs, or it is limited to the granules contained in cer- 

 tain peculiar cells, the parietes of which are also colourless, 

 which have received the name of pigment cells, and which we 

 are now about to describe. 



Pigment cells have precisely the same structure as those 

 of epithelium and epidermis, the description of which has 

 just been brought to a conclusion ; that is, they consist of cell 

 wall, nucleus, cavity, and granules ; the only difference be- 

 tween the two is, that the granules in the one case are 

 coloured, and in the other colourless: as may be inferred 

 from their similarity of organisation, a similar mode of de- 

 velopment prevails in both.* 



All the varieties of colour of the eye and of the skin ob- 

 served amongst the different members and families of the 

 human race depend upon the number of pigment cells and 

 the shade and intensity of the colouring matter enclosed 

 within the pigmentary granules ; the deeper the colour, the 

 more abundant the pigment cells, and the greater the depth 

 of colouring contained in the granules ; thus, of course, the 

 pigment cells scattered beneath the epidermis of the Ethiopian 

 are far more numerous than those found beneath that of the 



* Mondini (Comment. Bonon, t. vii. 1791, p. 29.) was the first observer 

 who made accurate microscopic observations on the pigment of the eye. 

 He stated that the pigment is not simply mucus, but a true membrane 

 formed of globules disposed in quincunx. The son all but completed the 

 work which the parent began : he found that each globule is made up of 

 little black points. Finally Kieser (De Anamorphosi Oculi, 1804, p. 34.), 

 described the pigmentary membrane as a cellular tissue containing cor- 

 puscles. 



