Electron microscopy of cytoplasmic structures in frozen-dried mouse pancreas

Mouse pancreas was prepared by a freeze-dry method and embedded in methacrylate in vacuo without the use of aqueous solutions, postfixation or staining. Ergastoplasm, mitochondria and zymogen granules were readily recognized. The ergastoplasmic sacs were oriented in an orderly, parallel array similar to that seen after osmium tetroxide fixation. The membranes of the sacs were of high density, but the ergastoplasmic granules characteristic of osmium tetroxide-fixed tissue were not visible. The narrow space outside the ergastoplasmic sacs contained a homogeneous material of high density, while the broader space inside the sacs contained discontinuous aggregates of lower density.