The tissue is fixed in a chemical preparation to preserve its morphology as much as possible. Various books contain descriptions of tissue fixation. Here, I will list a number of important points concerning tissue fixation.
- The entire brain is fixed in 10–20% formalin for 2–3 weeks. A normal undiluted formalin solution consists of 37–38% aqueous formaldehyde solution. Thus, 10% formalin consists of approximately 4% aqueous formaldehyde solution.
- Fix the brain in a large amount of formalin.
- Ensure that the fixation time does not extend over a long period.
- Change the fixative solution a number of times (change at least once after autopsy).
- Take the following steps to ensure that the fixative solution penetrates into the deep parts of the brain and is not simply on the surface:
Suspend the brain in the fixative solution to ensure that the bottom surface of the brain does not adhere to the bottom of the fixing container.
Comply with applicable laws and regulations when handling formalin and consider the work environment.
- Make a slit in one section of the corpus callosum
- Make a slit in the pia mater at the base of the brain
- Lift the cerebellum and make a slit in the pia mater around its border with the brain stem
（These steps will lead to complete fixation of the brain with respect to the basal ganglia and insular gyri by ensuring that the fixative solution fully penetrates the intraventricular area and Sylvian fissure, which will enable even staining at a later date.）