Identification of glycogen in thin sections of amphibian embryos.

Embryonic amphibian cells when examined with the electron microscope were observed to contain an abundance of small particles, approximately 325 A in diameter. The periodic acid/ Schiff reaction and enzymic digestion were employed to determine the nature of the particles, and from the results of these tests they were concluded to be glycogen. Treatment of thin sections with periodic acid/lead citrate solutions resulted in a marked increase in contrast of the glycogen particles compared with other cell structures, and in a clearly defined substructure of 40-A grains appearing within the particles. This differential staining method enabled the particulate glycogen to be distinguished from ribosomes.