Postnatal Changes in the Number of Mast Cells and PAS Cells in the Thymus of Mice

The postnatal development of mast cells and PAS cells in the thymus of mice was quantitatively studied with cytological and cytochemical techniques. Male mice of Strong A strain were divided into 9 age groups : newborn, 1, 3 and 4 weeks, and 2, 3, 6, 12 and 24 months of age. The number of mast cells and PAS cells contained in a 1mm?2 section of thymus, cut 5* thick, was estimated on aclain blue-PAS stained sections. A small number of CF# 1 strain mice were also examined to determine if there were any quantitative differences between the two strains.