There are many ways to preserve organs and tissues, but the most accessible and most commonly used method is that of Melnikov-Razvedenkov. After fixation in 5% or 10% formalin and subsequent washing with water, the macropreparation is mounted in a jar in the desired position. The following three solutions are used sequentially:
| I. Formalin 10% | 100 mL |
| Potash chloride | 5 g |
| Acetic acid potassium (Potassium acetate) | 30 g |
| Water | 1000 mL |
| II. Pure ethyl 96% rectified alcohol | 600 mL |
| III. Glycerin | 600 mL |
| Acetic acid potassium | 400 g |
| Water | 1000 mL |
The macropreparation is fixed in solution I until it stops releasing red blood, during which time the solution acquires a dirty brown color. The process takes from one to several days. The disadvantage of preservation in formalin is a color change of the tissues, since the hemoglobin in the blood is converted to methemoglobin, which is dirty brown, almost black color. To restore the natural color of the organs, a second solution (solution II) is used, which converts methemoglobin to stable cathemoglobin. Since the latter has the color of oxyhemoglobin, the preparations return close to their natural color. For permanent storage, preparations are placed in solution III, in which they are stored indefinitely and, in addition, remain suitable for microscopic examination (Fig. 1). The jars are not sealed hermetically, so that when the temperature rises, warm air in the vessel exits through small holes; when the temperature drops, cooler air enters the vessel in the same way. If the jar were to be sealed hermetically, when heated, not only could the lid peel off, but the jar itself could also burst.
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Fig. 1. Finished macropreparation