“…Toluidine blue is a metachromatic (a pH-dependent dye that stains cell elements a different color from the dye), staining heparin-containing granules purple or red [ 2 , 63 ]. As a simple, non-sensitive chemical, it can be applied to tissues after various methods of fixation and embedding [ 44 , 46 , 47 , 49 , 50 , 51 , 53 , 55 , 57 , 58 , 61 , 62 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 ]. However, its major disadvantage is the inability to distinguish immature from mature MCs, which could be done by alcian blue-safranin staining [ 45 , 48 , 67 , 72 , 93 ].…”