Method for preparing a sample

A method for treating a sample consisting of a biological tissue embedded in paraffin, the method comprising:

• bringing the sample into contact with a stream of a first compressed fluid to extract the paraffin, said first compressed fluid selected from liquid or supercritical carbon dioxide having a pressure between 4-70 MPa and a temperature between 0-50° C.;
• bringing the sample into contact with a second compressed fluid to impregnate the tissue to bring the tissue to a hydrated state, or to a state impregnated with a water-soluble substance, each of said states making the tissue capable of undergoing histological staining, without any damaging impairment of a structure of the tissue, said second compressed fluid comprising a mixture of carbon dioxide, water and a water-soluble organic solvent, said second compressed fluid having a pressure between 4-70 MPa and a temperature between 0-50° C.;
• evacuating the second compressed fluid gradually and in a controlled manner;
• and
• recovering the sample.