MELANOSIS. 249 



grey or white horses, are most commonly the subjects of this 

 disease. This opinion is certainly supported by the case related 

 by me, the horse being a white Arabian. He had one tumour 

 only externally percei)tible, which was about the size of a 

 walnut, and had existed for some years ; but he had an immense 

 number deeper seated in various parts of the body. ^ It will be 

 an interesting subject for future observation to ascei'tain whether, 

 and to what extent, his progeny are affected ; because, if they 

 really become aifected to any extent, it will offer a strong 

 objection to the use of these white horses as stallions. Lec- 

 turers and writers have but little to say on the treatment of the 

 disease, and that little not very satisfactory. It appears to me 

 that, amongst our remedial agents, the use of iodine demands 

 some attention. 



Melanosis appears to be a much more common disease in 

 India than in this country. In April, 1840, Mr. Jackson, of 

 the East India service, communicated the following paper on 

 the subject to the Veterinarian : — "I was pleased to find that 

 the conclusion I had come to in my own mind as to the identity 

 of the disease common among horses in India, known by the 

 name of ' diseased tail,' with ' melanosis ' in the human subject, 

 was confirmed by your intelligent correspondent, Mr. W. C. 

 Spooner. The disease, as described at pages 163 and 164. of 

 this journal, is very common about Madras, but in most cases is 

 confined externally to the tail, which is occasionally enormously 

 enlaro-ed. I have seen tumours round the anus, and in various 

 parts of the body. Light grey horses are most subject to it, 

 and of that colour those with curly manes and tails. I have 

 never had an opportunity of making a j^ost mortem examination : 

 for though cast when they can no longer bear the crupper, 

 horses affected with this disease do not generally suffer in health. 



" The treatment usually adopted is, to cut away the tumours 

 when practicable. I have seen Mr. Plooper, V. S., 4th regiment 

 Light Cavalry, take slices off a tail like a wheelwright would 

 from a spoke of a wheel. The skin soon healed over again, and 

 the tail looked quite respectable to what it did before. 



" I have never tried any internal remedy ; but I think, as Mr. 

 Spooner suggests, that iodine might be useful." — Eu.] 



CHAP. XLVL 



THE STRUCTURE AND FUNCTIONS OF THE EYE. 



[The eye may be appropriately regarded as an optical instru- 

 ment, by means of which pictures of external objects are trans- 

 ferred to the brain by the aid of the optic nerve and its expansion. 



