SYNOPSIS The production of 0 4,u thick, full-length sections from renal tissue taken by needle biopsy is achieved by formalin and osmic acid fixation and embedding in epoxy resin as for ultramicrotomy. The marked improvement in histological clarity by using this technique is illustrated by comparison with material embedded in paraffin.

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Pulmonary blastomas are extremely rare subpleural tumours consisting of relatively welldifferentiated branched tubular glands which resemble fetal lung tissue embedded in a malignant mesodermal stroma. The previous 13 established cases reported up to June 1969 are now supplemented by a fourteenth. The patient was a 32-year-old man who developed acute pain in the right chest followed by a haemorrhagic pleural effusion. At thoracotomy a yellowishwhite necrotic and vascular tumour was located lying loosely in the fissure between the upper and the middle lobes. The histological appearance of the tumour was unusual in that the mesodermal element was very variable and in different areas simulated fibrosarcoma, leiomyosarcoma, lipomyxosarcoma, and malignant haemangiopericytoma. This diversity of mesodermal proliferation is best explained on the basis that the tumour has originated in an embryonic or pleuripotential type of mesenchyme, the site of which is probably in the periphery of the lung.

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