248 DISEASES OF THE IIOKSE. 



followed weakness of the hind quarters, which, though slight at 

 first, gradually increased until the neck of the bladder was 

 paralysed, and rendered incapable of retaining the urine, which 

 flowed away as it entered the bladder. On passing my hand up 

 the rectum, 1 detected a large tumour, Avhich appeared to adhere 

 to the spine, and which, from pressing on- the nerves of the hind 

 extremities, accounted for their partial palsy. The animal was 

 destroyed, and the tumour was found of great size, not only 

 pressing on the nerves, but appearing within the cavity of the 

 large vein, the vena cava, the disposition and appearance of 

 which it had completely altered. On cutting into the tumour, 

 it was found to be melanosis, a disease that had not been pre- 

 viously noticed by any English veterinary author. 



Melanosis is defined by Laennec as " a pathological produc- 

 tion deposited upon the surface, or in the substance of an 

 organ, of a darkish or blackish colour, having no analogy with 

 the liealthy tissues of the body." The disease which was de- 

 scribed by Brugnini in 1781, as being hereditarily transmitted 

 among the horses of Chevasso, and which he termed hemor- 

 rhoids, was evidently melanosis ; it was usually developed around 

 the root of the tail and the anus. 



Some years later, in 1784, the same disease was observed at 

 Bresse Gollety. Latournelle transmitted an account of it in 

 1809. He says, " there supervened in a young stallion, on the 

 second year of his covering, black ' houtons,' or buds, around the 

 anus. They soon extended to the scrotum and sheath. They 

 were placed between the skin and muscles, at first as large as a 

 small nut, and they increased until they attained the size of a 

 pullet's egg ; they did not suppurate, and were insensible to the 

 touch. In a short time all the cellular tissue was similarly 

 affected, and the animal died. When cut into, a matter like the 

 grease of a cart wheel flowed out. All the progeny of this 

 stallion which had the same colour was similarly affected ; those 

 which were black, bay, roan, or iron grey, escaped." 



In 1806, Laennec communicated to the faculty the result of 

 his observations on the same subject, which has been further 

 elucidated by other writers since ; but much still remains to be 

 done for it. The tumour may either be a black, opaque, homo- 

 geneous mass, or may contain a darkish-coloured fluid. Gohier 

 saw a tumour of the kind in a horse weighing thirty-six pounds. 

 The opinions of most writers as to the composition of the mela- 

 notic substance agree that its black colour is owing to the 

 presence of a large quantity of carbon. Many persons are of 

 opinion that the black principle is an aberration of the pigment 

 destined by nature to be deposited elsewhere, as the rete muco- 

 sum, the choroid, the hair. It is said that persons with light 

 hair, and elderly persons whose hair is white, as well as light 



