The Time Factor in Initiation of Freezing and in Penetration and Propagation of Ice in Tissues of Mouse Limbs

摘要

The course of the invasion by ice of mouse limbs exposed to various ambient temperatures was studied by distinguishing three stages: the initiation of freezing, the passage of ice through the skin, and the propagation of the ice within the limb. At an air temperature of -25C excised limbs froze within four minutes; at -20C they froze within seven minutes; at-15C the proportion of limbs remaining unfrozen after a 40-minute test period varied from 7 to 40%. The time required for the passage of the ice front through the skin (using a model system in which the skin separated ice crystals from a layer of physiological saline) was less than two seconds at -9C; it was eight seconds at -4C, 160 seconds at-1.8C; above-1.8C penetration could not be induced. (The resistance of the fur to wetting seems to be an important impediment to 'seeding' through the skin.) Within the foot (attached to the body in this section of the research), ice traveled from the toes to the heel at rates of the order of 2 cm per second at -8C, 1 cm at 6C, 5 mm at -4C and 1 mm at -2C. Thus, in nature limbs may remain supercooled for long times at quite low temperatures, but the actual passage of the ice through the skin or through the tissues is rather rapid. (Author)