Islets contain four major types of endocrine cells:
Beta Cells - most common and secrete insulin.
Alpha Cells - second most frequent and secrete glucagon.
Delta Cells - secrete somatostatin.
PP Cells - secrete pancreatic polypeptide.
Gomori's stain was an early histochemical technique that distinguished between beta- and alpha-cells. Beta cells stain blue, while alpha cells stain pink. The other types of islet cells cannot be identified.