3.3 
Pituitary tumour histology in acromegaly. 
In section (a) using haematoxylin and eosin (H and E) stain, the eosinophils contain cytoplasmic granules. The illustration shows a tumour consisting entirely of such cells. In section (b), using periodic acid-Schiff and orange G (PAS-OG) stain, the acidophils stain yellow or orange and the nuclei stain black. This stain is less subjective than H and E. Section (c), an immunostain for GH in a GH secreting tumour, shows somatotrophs stained brown.