Tumoren

Osmium tetroxide fixation of tissue blocks, as usually effected, is preceded by an acidification of the tissue. This acidification is probably responsible for morphological alterations which are notably disturbing in electron microscopy. The acidification and the resulting morphological alterations cannot be prevented by homogenizing the tissue directly in OsO4 solutions or by adding enzyme inhibitors (fluoride, iodoscetamide) to the fixative. Fixation experiments with buffered OsO4 solutions have shown that the appearance of the fixed cells is conditioned by the pH of the fixative. The quality of fixation can be materially improved by buffering the OsO4 solutions at pH 7.3-7.5, The acetate-veronal buffer appeared to be the most favorable of the buffers tested, Because of these findings, 1 per cent OsO4 buffered at pH 7.3-7.5 with acetate-veronal buffer is recommended as an appropriate fixative for electron microscopy.

A description has been given of the pathologic changes produced experimentally in animals by the inoculation of a virus material obtained from a mouse with spontaneous encephalomyelitis. The most distinctive feature of the lesions in the central nervous system is the widespread destruction of myelin. Giant cells derived from a variety of tissue elements characterize the early lesions. The liver in the majority of cases is the seat of focal necrosis. In some mice, infected with large doses by the intravenous route, there is produced massive necrosis of the liver, with fat infiltration and calcification. Giant cells are occasionally found in lymphatic tissue, but no significant changes were noted in other organs. Inclusions or elementary bodies were not demonstrated in the lesions. Similar lesions were produced by the inoculation of mouse virus into hamsters. In rats, the lesions were of a more chronic character. The relation of this disease to other demyelinating diseases of man and animals is discussed.