1.Fix tissues with 10% formalin or other fixatives for 24-48 hours at room temperature. Make sure you have enough fixative to cover tissues. Fixative volume should be 5-10 times of tissue volume.
2. For routine stains where perfusion is not required, tissue is sectioned and drop-fixed in a 10% formalin solution. Fixative volume should be 20 times that of tissue on a weight per volume: use 2 ml of formalin per 100 mg of tissue.
3.Due to slow rate of diffusion of formalin (0.5 mm hr), tissue should be sectioned into 3 mm slices in cooled brain before transfer into formalin. This will ensure the best possible preservation of tissue and offers rapid uniform penetration and fixation of tissue within 3 hours.
Figure 2 : A surgical specimen fixing in formalin and ready for grossing. Note that there is a generous volume of fixative compared to the size of the specimens. A cassette that will contain the specimen during processing has already been printed with patient identifiers.