An apparatus (100) for processing a biological sample (101). The biological sample being arranged on a first planar surface (102) of a carrier (103). The apparatus comprises a second planar surface (104) arranged substantially parallel to said first planar surface and at a first distance from said first planar surface, said first planar surface and said second planar surface are arranged at an angle (A) greater than zero degree from the horizontal plane (HP); supply means (126, 131, 220) for supplying an amount (105) of a liquid that is to be applied to said biological sample. The first planar surface and second planar surface are configured to be arranged at a second distance from each other, said second distance being such that said supplied amount of liquid is distributed over said biological sample when said first planar surface and said second planar surface are brought to said second distance from each other.