Whole Mount Preparation of Chick Blastodermal Edge Tissue for Microscopic Examination

Three methods of preparation of chick blastodermal edge tissue for conventional microscopy were attempted: (1) Sections were cut from Water Wax (E. Gurr) embedded material. This method was unsatisfactory due to loss of morphological relationships produced by the inability to attach the tissue to a slide. (2) Frozen sections were cut from embryonic marginal tissue with its underlying white and yellow yolk which was embedded in a 25% gelatin solution. This method retained morphological relationships prior to 24 hr of egg incubation, but was technically impractical in excess of this period of incubation. Also, the gelatin could not be removed from the sections and cellular detail was obscured by its subsequent staining. (3) The blastoderm was removed from the yolk and adherent vitelline membrane, and the yolk dissected from a small piece of this blastodermal edge tissue under a dissecting microscope. The dissected tissue, primarily monocellular and dicellular in thickness, was transferred to a slide and attached to it by allowing a few drops of ether-alcohol (1:1) to flow over it. The plane of the tissue was, therefore, parallel with the plane of the slide. Most fixatives and staining techniques could subsequently be used. Fixing for 30-120 min in ether-alcohol (1:1) containing 0.5% glacial acetic acid gave excellent results with the staining techniques attempted. Fixation with Zenker's fluid for 24 hr followed by a 6 min hydrolysis with 1 N HC1 was best prior to the Feulgen technique.