A routine method for embedding animal tissues in Spurr resin for electron microscopy.

The epoxy resin epon 812 has been used in this department to embed a variety of normal and pathological tissues for a number of years. Unfortunately during the past 18 months sectioning qualities of polymerized epon blocks have become variable in an unpredictable manner. It is possible that the batch variation in the quality and composition of the dodecynl succinic anhydride (DDSA) could be responsible. In view of the unpredictable sectioning qualities of the epon currently in use it was decided to investigate the possibility of replacing the epon mixture with Spurr's (Spurr, 1969) resin.' This resin mixture is considerably less viscous than epon mixtures and consequently easier to dispense. The resin is also hydrophobic and wetting of the block face is not liable to occur. After several trials of embedding kidney in Spurr's resin it was apparent that it would be necessary to modify our sectioning and staining techniques. Of the number of drawbacks encountered with Spurr's resin, possibly the most serious was the poor staining of ultrathin sections. Thick (2 tm) sections for light microscopy would not adhere to glass microscope slides while being stained. Similarly ultrathin sections would not adhere to copper grids if these were used as received from the supplier. After extensive trials we were able to overcome these initial difficulties and use the methods described below.