A procedure is described for the preparation of ultrathin frozen sections of glutaraldehyde-fixed or unfixed islets of Langerhans by cryo-ultramicrotomy. Freezing of the tissue was accomplished by direct immersion of isolated islets in liquid nitrogen. Sectioning was performed at a specimen temperature of -80 °C and a knife temperature of -40 °C, the ribbon of sections being collected on a trough containing 60 % dimethyl sulphoxide. Staining was accomplished with 4 % silicotungstic acid and sections were protected from drying artifacts by rinsing with 0.5% polyethylene glycol.

Even in tissue not subjected to prior glutaraldehyde fixation, most of the structural features of A and B cells were well preserved in frozen sections, which were obtained in a number and quality which should render them suitable for ultrastructural, cytochemical or radioautographic studies.

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