A Modified Polyester Embedding Medium for Sectioning

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Abstract
A modified polyester resin designated as C. M. E. Tissue Support Resin can be cut on a rotary microtome and can yield sections from 5 to 50μ from tissue blocks that range from 5 to 16 mm in diameter. It is firm enough to support hard structures that lie adjacent to soft ones and retain all in their normal position. The resin-catalyst-promoter system cures oi hardens at a low temperature so that blocks are ready for cutting 6 hr aftei tissue has been routinely dehydrated. The resin is compounded from a plasticized rigid polyester and adjusted to a proper viscosity. Several grades of hardness can be attained by changing the formula. It has been tested with both soft and hard tissues, including limbs and tails of 7-mo old mice and mature whole grains of wheat, and provides a more substantial and more readily prepared embedding medium than celloidin. Sections can be stained before mounting, without removing the embedding material, with aqueous safranin O followed by fast green FCF in absolute alcohol. The plastic remains clear. Other staining processes require modifications to get good results.