A Procedure for Selective Differentiation of Epithelial Derivatives in Gross Blocks of Embryonic and Adult Tissues

¹ West Virginia University Medical Center, Morgantown, West Virginia
² Indiana University Medical Center, Indianapolis, Indiana

Material has been obtained from rhesus monkeys and human embryos, fetuses, and infants. For optimal results the tissue must he obtained as soon after death as possible. The vasculature is perfused with warm heparinzed mammalian Ringer's solution followed by 10 per cent neutral formalin for fixation. Blocks of selected tissue 1 cm. thick are hydrolyzed in 4 per cent KOH for 6 to 8 days, then transferred to solution No. 1 composedly of 1.5 parts glacial acetic acid, 5.5 parts distilled water, and 1 part glycerin for 24 hours. Tissue is then stained in a solution of 1 part Ehrlich's acid hematoxylin, 1 part glycerin, and 6 parts of distilled water for 5 hours; it is then immersed in solution No. 2, composed of 1 part glycerin and 7 parts of distilled water, for 8 hours, while excess stain diffuses out of the tissue. Dissection and trimming are done in solution No. 2. Dehydration is accomplished in ethylene glycol monoethyl ether (or the standard alcohol series) and clearing in sending solutions of 25, 50, and 75 per cent of methyl salicylate (or silicone oil) in ethylene glycol monoethyl ether. If destaining see figure in pdf is necessary, the tissue is run back down through the clearing solutions and into 2 changes of the dehydrating solution. It is then placed into solution No. 1 for destaining, after which it is again dehydrated and cleared. The tissue may be examined or stored permanently in either the methyl salicylate or the silicone oil. Epithelial structures, visualized as whole anatomical units, appear well differentiated and stain a dark blue, while the connective-tissue stroma around them is stained lightly or not at all.