Fixation can broadly be classified into two general types – Physical and chemical.

Physical fixation techniques include heating, microwaving, and freeze-drying or cryo-preservation. These methods work by denaturing the proteolytic enzyme and preventing autolysis. Physical fixation techniques preserve the sample’s morphology but not its internal structures. 

Chemical fixation involves immersing the sample in a fixative that helps to prevent autolysis and preserve the tissues in their original state.