An automated apparatus for treating biological specimens, comprising: a plurality of independent operable reaction modules, each reaction module comprising: a reaction compartment (112; 212) having an inner space; a slide support element (114; 214) able to support at least one microscope slide (140; 250) in a horizontal position, the slide support element movable independently of the other slide support elements into and out of the corresponding reaction compartment for positioning the microscope slide in the reaction compartment or for removing the microscope slide therefrom; reagent dispensing means (154, 14, 44) for dispensing a reagent to the microscope slide when the microscope slide is disposed on the slide support element; and sealing means (144, 145; 244, 246) for forming a pressure-tight seal for sealing the inner space of the reaction compartment; characterized in that the apparatus further comprises: pressurizing means for pressurizing the inner space of the reaction compartment after the inner space has been sealed by the sealing means wherein the reaction compartment is pressurizable independently of each of the other reaction compartments, the pressurizing means comprising heating means (136, 164; 248) for heating a reagent dispensed from the reagent dispensing means onto the microscope slide disposed on the slide support element to a temperature in a range of 100°C to 350°C; and a microprocessor able to control the pressurizing means to maintain a pressure within the inner space of the reaction compartment in a range of from above atmospheric pressure to 2514 kPa (350 psig). a plurality of independent operable reaction modules, each reaction module comprising: a reaction compartment (112; 212) having an inner space; a slide support element (114; 214) able to support at least one microscope slide (140; 250) in a horizontal position, the slide support element movable independently of the other slide support elements into and out of the corresponding reaction compartment for positioning the microscope slide in the reaction compartment or for removing the microscope slide therefrom; reagent dispensing means (154, 14, 44) for dispensing a reagent to the microscope slide when the microscope slide is disposed on the slide support element; and sealing means (144, 145; 244, 246) for forming a pressure-tight seal for sealing the inner space of the reaction compartment; a reaction compartment (112; 212) having an inner space; a slide support element (114; 214) able to support at least one microscope slide (140; 250) in a horizontal position, the slide support element movable independently of the other slide support elements into and out of the corresponding reaction compartment for positioning the microscope slide in the reaction compartment or for removing the microscope slide therefrom; reagent dispensing means (154, 14, 44) for dispensing a reagent to the microscope slide when the microscope slide is disposed on the slide support element; and sealing means (144, 145; 244, 246) for forming a pressure-tight seal for sealing the inner space of the reaction compartment; characterized in that the apparatus further comprises: pressurizing means for pressurizing the inner space of the reaction compartment after the inner space has been sealed by the sealing means wherein the reaction compartment is pressurizable independently of each of the other reaction compartments, the pressurizing means comprising heating means (136, 164; 248) for heating a reagent dispensed from the reagent dispensing means onto the microscope slide disposed on the slide support element to a temperature in a range of 100°C to 350°C; and a microprocessor able to control the pressurizing means to maintain a pressure within the inner space of the reaction compartment in a range of from above atmospheric pressure to 2514 kPa (350 psig). pressurizing means for pressurizing the inner space of the reaction compartment after the inner space has been sealed by the sealing means wherein the reaction compartment is pressurizable independently of each of the other reaction compartments, the pressurizing means comprising heating means (136, 164; 248) for heating a reagent dispensed from the reagent dispensing means onto the microscope slide disposed on the slide support element to a temperature in a range of 100°C to 350°C; and a microprocessor able to control the pressurizing means to maintain a pressure within the inner space of the reaction compartment in a range of from above atmospheric pressure to 2514 kPa (350 psig).