Definition. Melanin, in normal tissues, abnormal. Melanosis.
Bisulphide of carbon subcutem. Decomposition of hæmoglobin in
leucocytes. Coloration of tissue.
_Definition._ Accumulation of granules and scales of blood pigment
(melanin) in the circulating fluid, and in various organs (spleen,
liver, bone marrow, brain, etc).
=Melanin=—C_{44.2}, H_{3}, N_{9.9}, O_{42.6}—or black pigment (a close
relative of hæmatin) occurs physiologically in epithelium (choroid,
retina, iris, in the deeper layers of epidermis, and on the surface of
the dog’s lung and of the sheep’s brain) and in connective tissue
corpuscles (lamina fusca of the choroid).
Pathologically it is found in the blood of the victims of malarious
fever, often in great abundance, and in the spleen, liver, bone marrow,
brain, lymph glands and some other organs. It is formed abundantly in
the black pigment tumors (melanosis) of man and animals, and in
extensive melanosis is present in the blood of both man and horse
(Schimmeln). So far it has not been found in connection with the
extensive destruction of red globules which takes place in anæmia.
Schwalbe has developed malanæmia experimentally by the hypodermic
injection of bisulphide of carbon in rabbits.
According to one view the melanin is produced in connection with the
destruction of red globules in the liver, spleen, etc., and is thence
carried into the blood. This is in keeping with the local formation of
the pigment in melanosis. Arnstein however urges that in malarious cases
the destruction of the red cells takes place in the blood, and that the
hæmoglobin, absorbed into the leucocytes, is transformed into melanin,
and finally deposited in the tissues by the migrating white corpuscle.
Why the hæmoglobin set free in anæmia is not similarly transformed, does
not appear. The pigmented organ may be quite black in the immediate
vicinity of the blood vessels, and in its general aspect in chronic
cases reddish brown, dark gray, or dark olive.