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Mast cells in the chick digestive tract. I. Development.

Mast cells in the digestive tract of the developing chick embryo were studied with histochemistry and electron microscopy (EM). The cells appeared in the esophagus, proventriculus and small intestine on about the 13th day of incubation, whereas mast cells in the tongue appeared earlier. The staining properties and ultrastructure of the mast cells varied with development. In 13- and 15-day embryos, mast cells showed a pale metachromasia with toluidine blue, and stained blue with Alcian Blue-Safranin O (AB-S). In the 18-day embryo, mast cells stained a deep purple with toluidine blue. Stained with AB-S, most of the mast cell granules stained blue, but some red granules were also seen in a few cells. In the newly hatched chick, the cells stained a strong reddish purple with toluidine blue. Stained with AB-S, a few cells contained only blue or red granules, but most contained both. Observations with the EM revealed that the internal structure of the granules varied with the stage of embryonic development. The basis for the changes in staining properties and ultrastructure of the mast cell in the developing chick embryo were discussed.