Pigmentation. 209 



Pigmentation. 



Autochthonus Melanosis. — Normally the epithelial cells of 

 the cuticle, especially the deeper layers of the rete ^Malpighii, the 

 hairs and horns, the epithelium of various ingrowths from the 

 skin (for example, the mouth in dogs), besides the pigmented 

 epithelium of the retina and many ganglion cells, and in a num- 

 ber of situations the connective tissue elements (the cells of the 

 choroid, sclera, pia, and also the cutis), contain in variable 

 amounts coloring substance in the form of _\ellow, brown or 

 black granules (the former ha-niofusciii ; the latter, melanin). 



The origin and formation of this pigment are as yet not en- 

 tirely clear. The entire lack of similarity to blood pigment, 

 especially the absence of iron as a constituent, the pigment granules 

 being, however, rich in sulphur and containing nitrogen 

 (v. Nenski, Sieber, Abel, Davids and Schmiedeberg), would in- 

 dicate that these granules are transformed from the albuminates 

 formed within the cells as products of a peculiar ("metabolic," 

 from fiera^dWeLv , to transform, to change) cellular activity. It is 

 not known whether the material employed in the pigment pro- 

 duction is originally derived from the blood or whether it repre- 

 sents an excretory substance of the system and its production is 

 comparable to the formation of humus ; it can only be said that 

 in the same way as in early foetal life and tlience onward, forma- 

 tion of blood coloring matter takes place from the influence of 

 cellular activity, or as. under the influence of light, chlorophyl 

 formation is a form of cellular function, these pigments are de- 

 veloped within the cells. 



Connective tissue cells have been noted in the linman coriuni loaded 

 with pigment and capable of movements which actually carry the pigment 

 into the epithelial ceils, and in some circumstances carry it away again 

 ichro)natoplu->rcs). This has been observed particularly in connection with 

 experimental transplantations; where a small bit of white skin has been 

 grafted upon a black (negro), after healing it becomes as dark as the 

 neighboring tissue from the penetration of chromatophores, and vice versa 

 in transplanting black skin upon a white person, loss of color takes place 

 in the graft by convection of the pigment through the agency of the 

 wandering chromatophore cells to the lymph glands. (The existence of 

 these wandering cells has been doubted by Kromayer.) According to 

 C. Gessard, the black pigment, especially of melanotic tumors, is produced 

 from oxidation of tyrosin (by an oxygenating diastase called tyrosinase") 



An increased accumulation of autochthonous pigment, a liypcr- 

 pigmentosis or hyperchromatosis, occurs in the human skin in the 



