Formic Acid Corrosion for the Demonstration of Pulmonary Elastic Tissue

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Abstract
By a revised technique, human pulmonary elastic tissue can be isolated in a form suitable for examination under the stereoscopic microscope. Fresh human lungs from autopsy are fixed by intrabronchial infusion with 10% formalin for 24 hr. Slabs 1.5 cm thick are cut and the formalin removed in running water. One such slab is embedded under intermittent vacuum in an aqueous mixture containing 15% gelatin, 10% glycerol, and 1% phenol; then allowed to gel. Frozen sections 2 mm thick are cut on a large-section MSE sledge microtome. Squares 3 × 3 cm from such a section are corroded for 4-5 days in 88% formic acid at 45 C, washed once with distilled water, and mounted in glychrogel containing 6% gelatin. The elastic tissue network of the lung will have been freed from surrounding elements. The preparation should be stored in a refrigerator. Blocks for thin sections and large thick un-corroded sections can be prepared from the same lung as part of an over-all procedure.