PRINCIPLES OF VETERINARY SURGERY 527 



and partly dissolves it. Nitric acid reddens the granules 

 and to some extent dissolves them. 



Melanin is found in the cells of the choroid, the ciliary 

 processes and the iris, in the form of fine pigmentary gran- 

 ules. It is found, more or less abundant, according to the 

 region of the body and the species of animal, on the surface 

 of the derma (under the epidermis) in the epithelial cells, 

 and rarely in the form of free granules. Numerous investiga- 

 tions, which cannot be reiterated here, have been made by 

 Thenard, Clarion, Lassaigne, et. al. Some have found iron 

 and sulphur, while others found only sulphur as the mineral 

 constituent. 



The fact is there are iniinite varieties of melanin as there 

 are infinite varieties of egg albumen or coloring of grapes, 

 a fact found in history of many complex substances. Its 

 component parts are albuminoids, sulphur and sometimes 

 iron. Brandt and PfeifTer found 0.424 to 0.625 per cent, 

 and Morner 0.075 to 0.2 per cent of iron in their analyses, 

 which shows that composition is rather variable. Bard and 

 Hugouneng found : 



Carbon 46 to 58 per cent. 



Hydrogen 4 to 5 per cent. 



Nitrogen 75 to 13.5 per cent. 



Oxygen 25 to 33 per cent. 



Sulphur . . .' o to 10 per cent. 



Iron Often 



The melanin of the choroid contains neither iron nor sul- 

 phur. Melano-sarcoma of the horse contains a pigment 

 called hippomelanin, which contains no iron and has the fol- 

 lowing composition : 



Carbon 53 to 55.5 per cent. 



Hydrogen 3.7 to 3.9 per cent. 



Nitrogen 10.5 to 10 per cent. 



Oxygen 28 to 32 per cent. 



Sulphur 2.7 to 3 per cent. 



