Abstract
Histochemical procedures were used to compare the constituents of frog and rat mast cells. On the basis of staining with acidified toluidine blue and the Alcian Blue-safranin combination, a substance characterized as heparin in rat cells was identified in frog mast cells. In contrast to their presence in rat cells, no histamine, serotonin or catecholamines could be observed in frog mast cells with the o-phthalaldehyde and paraformaldehyde reactions. A search for activities of two proteolytic enzymes, chymotrypsin-like and trypsin-like esterases, in frog mast cells was unsuccessful. β-Glucuronidase, N-acetyl-β-