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Summary Biopsy specimens of the terminal duodenum obtained from 11 patients with hereditary haemochromatosis were examined by light and electron microscopy. Stainable iron was found in the lamina propria of the terminal duodenum in only 4 patients, all of whom were in an advanced stage of the disease. The iron was localized in the basal parts of the villi, sparing their tips, and between the crypts of Lieberkühn. The iron-storing cells could be identified as plasma cells, in which ferritin and haemosiderin were localized within lysosomes and ferritin molecules scattered in the cell sap. There was no storage of iron in macrophages. These observations demonstrate the impaired iron-storing capacity of macrophages in hereditary haemochromatosis, which may be related to the increased iron absorption in this iron storage disease.

Summary Impulsecytophotometric and histocytological studies of the bone marrow of the rat were conducted after the administration of Daunomycin. The impulsecytophotometric survey revealed 24 hrs after administration of the drug an accumulation of cells in the G2 phase (29% in G2 + M compared to the control value of 12%) and a decrease of G1 cells from 65% (control) to 53%. The decrease in G1 cells is in a good correlation with our morphological studies showing a marked reduction of nuclei containing precursors of erythropoiesis. There is no morphological basis for the detection of the accumulation of cells in G2. An increase in the percentage of the cells in S phase 48 to 120 hrs after administration of the drug could be attributed to a regeneration phenomenon after cytostatic treatment and morphologically corresponds to a myelocytic bone marrow.

The peripheral myelinated nerve fibre was investigated by means of a light microscopical technique using plastic embedded 1 µ sections. The investigations were carried out on the sciatic nerve of the rat and were completed by electron microscopical observations. Special interest was focussed on the paranodal apparatus and the Schmidt-Lantermann clefts.

Presence and distribution of Schmidt-Lanterman clefts in relation to the thickness of myelin sheaths were studied with the use of a particle-size-analyser in Rhesus monkey and frog sciatic nerves. For this purpose the myelin sheaths were subdivided into classes of exponentially increasing diameter. The number of clefts per unit length significantly rises with increasing thickness of the myelin sheaths.