Tissue freeze-drying with a closed drying tube stored in a freezer

A simple method of freeze-drying tissue is described that does not require a continuously running vacuum pump. After the frozen tissue is positioned a few centimeters from the dessicant in a drying tube, a vacuum pump is attached briefly to lower the pressure in the drying tube. The drying tube is closed at a pressure of 5 X 10(-3) mm Hg or less, and the tube is stored in a freezer set at the desired temperature. Frog kidneys, 300-400 mg, were dry in about 24 hr at -32 degrees C and 48 hr at -40 degrees C. Since the tissue is dried in individual drying tubes, many tissue samples can be dried at one time.