Abstract
1. In the mast cell, the staining of metachromatic granules is influenced by the pH of the solution—at a level of pH 3 metachromatic granules stain rapidly, and orthochromatic staining is retarded.
2. The presence of metallic cations delays granule staining, the duration of the delay being proportional to the cationic concentration, related to the cationic valency, and to the position of the cation in its valency group.
3. Granule staining is unaffected by the addition of metallic cations to the "pretreatment" solution, and accelerated by temperature increase.