Black Mice Normal condition Melanosis is a normal condition found in many mammalian species where there is deposition of melanin pigment in various organs. This presents as rather spectacular black and brown spots of irregular shape. Part or all of the spleen may be heavily pigmented. Microscopically, the pigment is darker than hemosiderin and affected cells have a characteristic elongated appearance.
Melanin remains dark brown while iron based hemosiderin turns blue.
Diagnosed strains Table 1. Strains diagnosed with splenic melanosis. The Jackson Laboratory.