Modification of Johnson's method for metachromasia (toluidine blue) for testicular interstitial tissue

A modification of the Johnson's toluidine blue method for identification of testicular interstitial tissue elements is described. This consists in placing the tissue sections in Van Gieson's solution for 2 min after a 3 min immersion in an aqueous toluidine blue solution. Sharp histological distinctions between Leydig cells, mast cells and other connective tissue elements are obtained. The rounded Leydig cells with a large central nucleus and a prominent nucleolus show grayish yellow cytoplasm. The heterochromatin of Leydig cells nuclei stain a deep rose meanwhile its euchromatine is grayish yellow. Mast cells are full of large violet metachromatic granules which obscure nuclear and cytoplasmic features. Finally, fibroblasts and connective tissue collagen fibers stain yellow and pink respectively. An important advantage of this method is that the interstitial tissue components, specially the Leydig cells, retain the stain for a year or more.