Studies on golden hamsters during cooling to and rewarming from body temperatures below 0° C - I. Observations during chilling, freezing and supercooling

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Abstract
Hamsters narcotized by chilling in closed vessels to colonic temperatures between + 20 and + 15°C were subsequently cooled by immersion in melting ice and finally in fluid at — 3 to —14° C. Breathing ceased at colonic temperatures between + 6 and +2°C , and heart beats were arrested between + 2.5 and + 0.8°C. During immersion in sub-zero baths some of the animals froze progressively while the colonic temperature stabilized at a plateau between — 0.6 and — 1.0°C. The intra-thoracic temperature reached the same level shortly after. The cerebral temperature dropped to a slightly lower level. The subcutaneous tissues were several degrees colder than the internal organs. Other hamsters became supercooled and the trunk and extremities remained flaccid while the colonic temperature continued to fall, in some instances to as low as — 5 or — 6°C. The temperature in other regions fell in parallel; the thorax was approximately 2°C warmer and the brain and subcutaneous tissues 2°C colder than the colon. Supercooling was terminated in some animals by spontaneous crystallization accompanied by an abrupt rise in the temperature of the colon and other parts to the levels characteristic of freezing within them. The tendency to supercool was greater among hamsters which had previously ingested propylene glycol than among those on a normal diet. It was also influenced by the body temperature of animals at the time of immersion in sub-zero baths and on the initial bath temperature. The results of resuscitating frozen and supercooled animals will be described in part II.
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