Hematoidin, similar to bilirubin, is a reddish-brown pigment, found in the form of rhombic crystals; does not contain iron, is insoluble in water, alcohol, or ether, but is soluble in chloroform. It is found at the seat of old hemorrhages, and is generally considered a later form of hemosiderin.
The causes of hematogenous pigmentation can be divided into local and general.
Hepatogenous pigmentation is due to the presence of pigments derived from the bile, bilirubin, which is similar to hematoidin, and its oxidation product, biliverdin. The bilirubin is formed by the hepatic cells from hemoglobin, from destroyed red blood-cells, the iron being retained in the liver and not cast off along with the pigment. It is soluble and consequently is taken up by the blood and carried throughout the body, giving rise to the discoloration known as icterus or jaundice. Both cells and intercellular substances may be diffusely stained, or, if the condition is of long standing, greenish-yellow crystals or granules may be found.
The fluids of the body will also be discolored.
The presence of these pigments can be recognized by Gmelin's test with fuming nitric acid, which will give a play of colors at the point of contact.
This condition may be caused by (1) obstruction to the outflow of bile through the ducts, obstructive jaundice; (2) possibly through excessive bile formation resulting from hemolysis, hematogenous jaundice; (3) hepatic disorders, as acute yellow atrophy of the liver.
Metabolic pigmentation or melanosis is a discoloration of the tissues through the formation of melanin by the cells.
The tissues are colored yellow, brown, or black.
Under the microscope melanin occurs as dark granules in the cells and intercellular tissues. Is normal in the pigmented cells of the retina, choroid, hair, and skin.
Fig. 11. - Brown Atrophy of the Heart-muscle in Longitudinal Section (Dürck).
Its chemistry is not well known. It contains sulphur, but little or no iron, is insoluble in water, alcohol, and ether, but soluble in boiling alcohol, acids, and alkalis.
It is found commonly in the melanotic sarcoma. It generally tends to destroy the cells in which it is contained, and for some reason such tumors are generally more rapidly metastatic and fatal than the non-pigmented forms.
Fig. 12. - Anthracosis of the Lung. X 100 (Dürck).
The lung tissue is very much indurated as the result of newly formed connective tissue in which are embedded star-shaped masses of fine, granular, blackish pigment of inhaled coal particles.
In Addison's disease there is a general bronzing or melanosis of the skin. In many cases this condition seems to follow extensive disease of the adrenals.
In malaria the pigment present is probably not melanin, but is similar to hematin, and is formed by the action of the malarial parasite upon hemoglobin.
Certain muscular degenerations, as in "brown atrophy" of the heart. Is questionable whether such granules are true melanin. Various skin affections, as freckles, or lentigo, chloasma, and also in pigmented moles.
Extraneous pigmentation results from the introduction of coloring-matters into the body from the outside. The tissues most commonly affected are those of the lungs, giving rise to the condition known as pneumonokoniosis.
Anthracosis, or the deposition of coal-dust, is the most frequent, the lungs being colored more or less black according to the amount present.
Siderosis results from the inhalation of fine particles of iron.
Chalicosis, caused by the presence of lime in the lungs.
Argyria is a bluish-gray discoloration of the skin resulting from the long-continued use, internally, of nitrate of silver.
Tattoo marks following the introduction of insoluble coloring substances into the skin.