Melanoma. Black pigment tumors are especially common in gray and white horses. Their common seat is on the black, hairless portions of the skin (anus, vulva, perineum, tail, sheath, mamma, eyelids, lips, etc.), and secondarily in the lymph glands and spleen. In the latter they may grow to an extreme size, Wehenkel having mentioned one specimen of 60 pounds. Its surface is marked by uneven, rounded black swellings, the entire organ, indeed, seeming to be a conglomerate of these masses. The intimate structure is that of a sarcoma, so abundantly charged with black pigment granules that these appear to make up the greater part of the mass.
Rupture of these neoplasms with the escape into the abdomen of blood highly charged with the melanic matter is not uncommon.
The symptoms of the splenic deposits are not usually recognizable, but indications of chronic abdominal disease in connection with external melanotic formations may well lead to a reasonable suspicion.
Angioma. In a horse’s spleen weighing 30 lbs., there were numerous soft nodules of a deep cherry color. These were cavernous masses with connective tissue walls and the meshes filled with blood.
Similar vascular cavernous tumors have been found in the cow.
Lymphadenoma has been found in the spleen of horses and cattle in connection with the same disease of the lymph glands.
Like the other splenic tumors this is obscure and usually only found after death. The existence of adenoid swellings elsewhere conjoined with excess of white globules and indications of abdominal pain would be suggestive of splenic disease.
AMYLOID DEGENERATION OF THE SPLEEN.
Amyloid: horse: with exhausting diseases. Waxy secretion staining mahogany brown with iodine. Gangrene: Swine. Tubercle and glander nodules.
This has been occasionally detected in the spleen of the horse. It is usually connected with longstanding suppuration especially of bones, with advanced tuberculosis or other exhausting disease. The organ is usually greatly enlarged and the affected parts are firm, resistant and swollen. On section it has not the soft friable or pulpy appearance of the spleen, but an uniform waxy looking consistency, grayish or sometimes stained with blood. On the application of a solution of iodine and iodide of potassium the healthy splenic tissue is colored yellow, while the amyloid portion becomes of a deep mahogany brown.