comprises two serially connected cooling circuits 43 44 in which the first cooling circuit 43 serves for pre cooling and the second cooling circuit 44 then runs via the evaporators 7 10 in the specimen holder 4 and in the knife holder 8 and also via the plate evaporator 29 the first cooling circuit 43 has a liquefier 39 which runs via a throttle 42 or a capillary into a coaxial heat exchanger 38 and via a compressor 37 runs back into the liquefier 39 the coolant for the second cooling circuit still to be described is pre cooled in the coaxial heat exchanger 38 by the first cooling circuit 43 the coaxial heat exchanger 38 then acts like an evaporator for the first cooling circuit cooling the evaporating coolant in the second cooling circuit 44 the second cooling circuit 44 is constructed similarly to the first as is usual in refrigerators throttles 40 41 or capillaries are provided the outlet of which is then connected to the plate heat exchanger 29 and the evaporator 10 in the knife carrier 8 or to the evaporator 7 in the specimen holder 4 the outlets of the evaporators 7 10 are likewise connected to a compressor 36 which then pumps the compressed vapor phase coolant to the liquefier 39 the two part cooling circuit just described has the particular advantage that.