The pancreas is a mixed exocrine and endocrine gland. Most of the pancreas (~95%) is exocrine cells that secrete digestive enzymes into the duodenum. Scattered throughout the pancreas are clusters of only a few cells to several thousand cells (2 to 5%) that secrete hormones into the blood that regulate glucose.
Aldehyde fuchsin stains insulin in the beta cells of islets of Langerhans a dark purple. This allows beta cells to be distinguished from other islet cells. The exocrine pancreas stains a reddish-orange.