Iron, nitrogen, and protein content of the hemosiderin granules varied over a wide range. Electron microscopy of sectioned granules revealed aggregates of dense particles of different shapes, with diameters ranging from 10 A to about 75 A. In some of the granules dense particles corresponding to the iron hydroxide micelles of ferritin molecules were abundant. But many of the granules contained very few of these molecules.

The presence of ferritin and apoferritin in the samples of hemosiderin granules was demonstrated by means of precipitin tests in agar-gel, using rabbit antiferritin sera with known antibody nitrogen concentrations. At least three antigenic components were detected in highly purified crystalline ferritin prepared from tissues of the three patients; the hemosiderin granules contained the same antigens, but probably in much smaller quantities. Both ferritin and apoferritin molecules were extracted from hemosiderin granules, and were demonstrated in the electron microscope after suitable preparation.

The solubility curve of human ferritin in solutions of (NH₄)₂SO₄ was investigated. The results indicate that substantial quantities of ferritin or apoferritin can be lost in saline, aqueous media during isolation of hemosiderin granules from cells.

It was shown by means of electron microdiffraction on selected hemosiderin granules that the dense particles represent forms of partly hydrated -Fe₂O₃. The conditions necessary for electron microdiffraction in an electron microscope precluded an exact determination of the state of hydration of the -Fe₂O₃ or of its structural relation to (FeOOH) micelles of pure ferritin in its undenatured state.

The findings were considered in the light of evidence on the structure and disposition of hemosiderin in situ in cells, and on the structure of ferritin. Differences between endogenous hemosiderin and hemosiderin derived from injections of colloidal iron compounds were pointed out. The evidence indicates that in hemochromatosis and in secondary hemosiderosis much of the inorganic storage iron in liver and spleen is derived from degraded ferritin.

The findings suggest that an abnormal cellular metabolic pathway of ferritin is implicated in the pathogenesis of hemochromatosis and transfusional hemosiderosis.