MARCANO solution is used in medical diagnostics and histology, especially for microscopic counting of erythrocytes in lizard blood, such as that of iguanas. It is composed of formaldehyde (H2CO), which acts as a fixative and preserves cell structures, tri-sodium citrate dihydrate (Na3C6H5O7.2H2O), which acts as an anticoagulant and prevents clumping of blood cells, and sodium chloride (NaCl), which regulates osmotic pressure and contributes to cell stability. Due to its chemical composition, the solution enables permanent fixation and accurate counting of red blood cells. In scientific laboratories, the use of this solution can lead to accurate, consistent and repeatable results by allowing the preservation and visualization of the morphological characteristics of the erythrocytes.