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Electron-microscopic studies were conducted to observe ultrastructural changes during differentiation of eosinophilic granulocytes in carp (Cyprinus carpio L.). Differentiation at the myelocyte stage was found to relate to specific granules made of dense and light fields. By maturation they assume a mosaic-like texture and in each granule of mature granulocytes, a light, central "internum" and a peripheral dense wrapper can be distinguished. The activity peroxidase and acid phosphatase is located in the internum and of peroxidase in the wrapper of the granules.

A comparative study was made of enteroendocrine cells in the larvae of bony fishes (Teleostei): carp (Cyprinus carpio L.), big head (Aristichyts nobilis Richardson), silver carp (Hypophthalmichthys molitrix Valenciennes), and atlantic salmon (salmo salar L.). Argyrophil cells demonstrated by the method after Grimelius were found in all examined fish species. They are located in the pyloric appendices, stomach and intestinal mucosa. Gastrin-immunoreactive cells demonstrated by the immunocytochemical method were located in the pyloric part of the stomach in all examined fishes, except for the atlantic salmon in which they were not identified. The first argyrophil cells were identified at the age of about 10 days, while gastrin-immunoreactive cells proved to appear 5-7 days later.

In an attempt to determine the optimal daily ascorbic acid requirement, the effect of different levels of ascorbic acid intake on collagen synthesis was studied in a double-blind experimental design. By use of electron microscopy, interproximal gingival tissue sections in subjects consuming between 20 to 35 mg of ascorbic acid daily were examined before and after the administration of tablets containing 70 mg of ascorbic acid. The results showed that practically all subjects were affected by progressive periodontitis with marked changes in the connective tissue of the gingival lamina propria. After six weeks of supplementation with ascorbic acid, differences in the shape and activity of fibroblasts in the regenerative tissue of lamina propria were observed. This has resulted in the increased number of collagen bundles in fibroblasts' periphery, increased tonofibril content and an enlarged number of desmosomes between adjacent cells. It is concluded that the obtained results, though suggesting that the optimal daily ascorbic acid intake should be set above the presently recommended 30-50 mg, have to be quantified by a more objective analytical method.