all heat loads are removed by cryocoolers. Biological microtome type Cryostats are used in medicine to cut histological slides. They are usually used in a process called frozen section histology (see Frozen section procedure). The cryostat is essentially an ultrafine "deli-slicer", called a microtome, placed in a freezer. The cryostat is usually a stationary upright freezer, with an external wheel for rotating the microtome. The temperature can be varied, depending on the tissue being cut usually from minus 20 to minus 30 degree Celsius. The freezer is either powered by electricity, or by a refrigerant like liquid nitrogen. Small portable cryostats are available and can run off generators or vehicle inverters. To minimize unnecessary warming all necessary mechanical movements of the microtome can be achieved by hand via a wheel mounted outside the chamber. Newer microtomes have electric push button advancement of the tissue. The precision of the cutting is in micrometres. Tissue are sectioned as thin as 1 micrometre. Usual histology slides are mounted with a thickness of about 7 micrometres. Specimens that are soft at room temperature are mounted on a cutting medium (often made of egg white) on a metal "chuck", and frozen to cutting temperature (for example at -20 degrees C). Once frozen, the specimen on the chuck is mounted on the microtome. The crank is rotated and the specimen advances toward the cutting blade. Once the specimen is cut to a satisfactory quality, it is mounted on a warm (room temperature) clear glass slide, where it will instantaneously melt and adhere. The glass slide and specimen is dried with a dryer or air dried, and stained. The entire process from mounting to reading the slide takes from 10 to 20 minutes, allowing rapid diagnosis in the operating room, for the surgical excision of cancer. The cryostat can be used to cut histology and tissue slide (e.g., for enzyme localization) outside of medicine, but the quality of the section is poor compared to standard fixed section wax mounted histology. Newer technology such as the Compresstome, a type of vibrating microtome, utilizes agarose tissue embedding instead of an optimal cutting temperature compound to eliminate the need for traditional cryostat freezing and may be used for improved quality sectioning. See also Lambda point refrigerator References Containers Cryogenics Vacuum flasks