Thin sections of embryonic avian bone decalcify during preparation for electron microscopy, creating a false impression of mineral distribution. The results of the experiments reported herein show that viscous embedding materials do not penetrate compact formed bone, and so, in thin sections, the calcium apatite crystals may be leeched out by water, both in the collecting trough and in aqueous solutions of stains used to enhance tissue electron opacity. To prevent decalcification, a simple technique is described in which the aqueous fluids that come in contact with thin sections are saturated with respect to calcium and phosphate ions, thereby preventing solution of the bone mineral. The theoretical basis of this technique is briefly discussed.

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