390 
MELANOSIS AND OSSIFICATION. 
tional cause may be inferred from its taking place in various parts 
of the same animal, and from its rarely, if ever, being found in one 
organ or tissue alone. It has been seen in the skin, liver, lungs, 
heart, spleen, kidneys, peritoneum, and pleura of the same animal. 
M. Foy informs us that, in a portion of a melanotic tumour taken 
from a horse, chemical analysis shewed it to consist of albumen, 
fibrin, a black colouring matter, water, oxide of iron, and a few 
other salts. 
The black colouring matter largely predominated, and seemed to 
be composed of a highly carbonized principle, probably altered 
crassamentum . 
The fact which has been already noticed, that this disease is 
chiefly met with in white or grey horses, favours the doctrine of its 
origin from constitutional peculiarity. 
Dr. Carswell remarks that this circumstance is also favourable to 
the theory which ascribes the origin of melanosis to the accumula- 
tion in the blood of the carbon naturally employed to colour differ- 
ent parts of the body, as the hair, choroid coat of the eye, &c. 
Professor Dick, I believe, maintains that the dark pigment which 
should be distributed generally through the hair is removed after 
its formation, and deposited locally, and accounts thus for the dark 
deposits witnessed in this disease ; and as we know that grey 
horses get lighter coloured as age comes on, most frequently be- 
coming quite white, and that the disorder seldom exists to any 
extent in young horses — at least we have no record of its occurring 
in such — these are circumstances which go far to favour this hypo- 
thesis. 
Another very ingenious theory has been advanced to account for 
the accumulation of this black deposit in the system. It having 
been observed by M Treviranus, in experiments made by him on 
frogs, that, when the bloodvessels were deprived of their nervous 
influence, a black matter resembling the pigmentum of the choroid 
coat was formed in the capillaries, and in several membranes: 
hence the inference that the black matter thus formed proceeded 
from the deposition of the carbonaceous particles, which, not having 
combined with oxygen, had not been eliminated from the blood in 
the form of carbonic acid, owing to deficient nervous power and the 
retarded circulation in the capillary vessels. 
In melanotic tumours there is little vascularity, and, conse- 
quently, haemorrhage does not follow their excision ; they appear to 
be deposits essentially of an inorganic character. 
It does not appear that they increase much in size under ordinary 
circumstances. They may exist for many years, especially when 
they make their appearance in young horses, without acquir- 
ing greater bulk or occasioning inconvenience : of this we have 
