The goal of fixation is to rapidly and uniformly preserve tissue in a life-like state. While
placing tissue directly in fixative works well for small pieces of tissue, larger specimens like
the intact brain pose a problem for immersion fixation because the fixative does not reach all
regions of the tissue at the same rate 5, 7. Often, changes in response to hypoxia begin
before the tissue can be preserved 12. The advantage of directly perfusing fixative through
the circulatory system is that the chemical can quickly reach every corner of the organism …