This is one of the most critical steps in tissue processing. This process should be accomplished with the minimum disturbance of the protoplas-mic organization within the cells, and a minimum disturbance and distor-tion of the cellular arrangement. In addition to killing the protoplasm, the process must be able to fix the undistorted structure and, further, be able to render the mass of material firm enough to withstand handling. Thus the requirements for a good preservation are as follows:
1 Kill the protoplast without distortion.
2 Preserve to fix the fine detail.
3 Harden the material.