In the process of making biological sections, in order to avoid tissue autolysis or damage by bacteria, and preserve its physical structure, once the tissue block is taken out of the living body, it should be immediately and properly disposed of. The treatment is fixation, usually by soaking the tissue in chemicals to preserve its morphology and chemical characteristics as much as possible.  The chemicals used to immobilize tissues are called fixatives. So how are they classified?  According to the composition of the fixing solution, it can be divided into single fixation, double fixation and multiple fixation. First, single fixation is only fixed with glutaraldehyde or starvation tetroxide, generally used for single-cell samples or permeable samples. Second, double fixation refers to the first use of glutaraldehyde or paraformaldehyde for pre-fixation, and then use osmium tetroxide for post-fixation, this method has good effect and is widely used. Third, multiple fixation refers to the combined use of three kinds of fixatives to achieve the purpose of complementing each other. The main purpose of this process is to truly preserve every detail of the ultrastructure of the cell at the molecular level, so that the slice structure is clearer and the morphology is more complete. 

Many laboratory researchers are accustomed to storing tissue wax blocks for a long time at room temperature after sectioning, and the tissue after sectioning is prone to antigen loss for long-term storage at room temperature.  Some studies have found that when sections are stored at room temperature for more than 3 months, immunohistochemical staining results are weakened or even negative. Therefore, some scholars have carried out new and old slice preservation time control experiments. 11 different tissue wax blocks were selected and 10 pieces were cut continuously for a total of 110 pieces per case, and placed in room temperature air for 1 month, 3 months, 6 months, and 1 year, and then the control experiment was carried out with new sections. The experimental results showed that when stored at room temperature for 3 months after wax sectioning, the sensitivity of antigens to most antibodies decreased by 50%, and the antigen loss of some sections was more. Most antibodies did not show positive results after 6 months of sectional storage, and only a few sections had weak positive expression after storage for more than 1 year, especially nuclear expression antigen loss was more prominent.  The reason may be related to oxidation, so in practical work, wax sealing sections and -20 degrees cryopreservation tissue sections can be used to avoid antigen loss, or paraffin tissue blocks can be stored at 4 degrees, and then sectioned when used, which can greatly reduce the antigen loss rate.

Tissue microtome is a kind of equipment for pathological section analysis of human tissues, animal and plant tissues. Tissue microtome are generally divided into rotary microtome and frozen microtome. Rotary microtome: It is used to slice by rotating the hand wheel. The wax block table is embedded in the metal clamp seat that can move up and down in the groove, and cuts the flat slice by pushing forward with the micro screw. Some rotary microtome are equipped with three knobs and a fastening knob on the head, which can deflect and tighten it in all directions, so as to adjust the section of the wax block. The cutting angle of the slicer can be adjusted. Because this microtome uses a heavy and large slicer knife, it generally does not vibrate when cutting hard tissue. The slice thickness can be adjusted from 1-30 microns to any thickness by the knob, and each gradient is 1 or 2 microns. The advantage of the rotary microtome is that the body is heavy, so it is more stable than the rocking microtome. It is very suitable for cutting paraffin sections. It can be ideal for cutting continuous sections and also for cutting large tissue blocks. 

Frozen sectioning method is the most commonly used sectioning technique in histochemistry, especially enzyme histochemistry, fixed or unfixed tissue samples can be frozen section, fresh tissue frozen sections for tissue intracellular enzyme preservation is also a commonly used sectioning method in immunocytochemical research, can better preserve a variety of antigens, especially the antigenicity of surface antigens.  1. PreparationClean up the test bench and instrumentsTurn on the cryomicrotome and pre-reduce the cryomicrotome to the required temperature (-15~-20 °C)Prepare the processed slides, blades, glue and medicines  2. Clamp the frozen tissue block on the microtome holder, start the rough advance and withdrawal button, turn the knob, and smooth the tissue. 3. Adjust the thickness to be cut, according to different tissues, in principle, it is a cell-intensive thin cut, and the fiber multicellular thin can be slightly thick cut, generally between 5 ~ 10μm. 4. Adjust the anti-coil plate. The key to making frozen slices lies in the adjustment of the anti-roll plate, which requires the operator to be careful and accurately adjust it well and adjust it to the appropriate position. When slicing, cut out a complete, smooth slice. When the cut tissue adheres to a clean slide, gently apply a gentle force in one direction to avoid wrinkles during the tissue spreading process, ensure the integrity of the tissue structure and the beauty of the section.