MELANOSIS. 425 



And, lastly, there is scarcely a tissue or an organ that melanosis 

 may not invade. It may, therefore, be safely concluded that 

 " melanotic or melanoid tumours are, with very rare exceptions, 

 sarcomatous tumours, modified by the formation of black pig- 

 ment in their elemental structures." It may also be mentioned 

 that melanotic tumours in the human being have their favourite 

 seats in or beneath pigmentary moles. 



Melanosis is, with very rare exceptions, confined to grey horses, 

 and becomes developed as they whiten with age. Its favourite 

 seat is on the under surface of the tail, around the anus or vagina, 

 or the perinaeum ; more rarely the scrotum, mammary gland, inner 

 surface of thigh, and on the nose or lips. These are merely its 

 outward manifestations ; for on dissection it may be found, either 

 in large masses or as small multiple tumours, in the mesenteric, 

 bronchial, deep inguinal, and lumbar glands, and in the spinal 

 canal. I do not think that there is any part of the body that may 

 not be affected by these tumours ; but I wish to confine myself 

 strictly to those cases that have fallen under my own notice. 



In some cases there are no external tumours. The dissection 

 of one case — death occurring from dropsy — revealed a melanotic 

 mass, weighing six pounds, situated in the bronchial lymphatic 

 glands. In another case a tumour was found in the inguinal 

 plexus of glands weighing above eight pounds, which, previous 

 to death, pressed upon the crural nerves, and caused paralysis. 

 In the majority of cases, however, there has been some outward 

 manifestation of the disease ; but in occult disease occurring in 

 grey or very light chestnut horses, the practitioner ought to con- 

 sider whether such disease may not be due to melanotic growths. 



The development of melanosis is looked upon as a new excre- 

 tory function, set up for the purpose of eliminating from the 

 system the pigmentary matter which is no longer required for 

 the purpose of tinging the hair. If it were true that the pig- 

 mentary matter was already formed in the blood, and only re- 

 quired to be appropriated by the structures to which it gave colour, 

 the supposition would be justified ; but the fact is, pigment is 

 not conveyed to a part, but is formed by the cells of the tissues 

 in which it is found, out of materials supplied by the blood. 

 We must, therefore, look upon melanosis as being due to an 

 exalted formative power in tlie cells of the tissue in which it is 

 found. When formed in the skin of grey horses, we can easily 

 understand that its pigmentary ceUs may be stimulated to in- 



