Mast cells in the chick digestive tract. II. Fixation, distribution, histochemistry and ultrastructure.

Mast cells in the chick digestive tract were investigated with different fixatives, histochemical methods and transmission electron microscopy. Carnoy's fluid was the best fixative for the chick mast cell. Fixation in formalin reduced the number of mast cells and dissolved the granules. Mast cells stained reddish purple with toluidine blue, and bright blue with Alcian blue-periodic acid schiff (AB-PAS). Staining with Alcian blue-safranin O (AB-S) resulted in some cells only containing blue or red granules, and others containing both blue and red granules in the same cell. The result of AB-S staining was obviously affected by fixation. The ultrastructure of chick mast cells was described. Internal large granules had a variable morphology; some higher or lower electron density with a homogeneous appearance; some were finely granular; some had a mottled appearance, and a few showed a reticular structure. The distribution of mast cells varied. The proventriculus was the most abundant in mast cells among the organs examined. Only one type of mast cell was found in the chick digestive tract. The fixation, staining and the ultrastructure of chick mast cell granules were discussed.