SUPERCOOLING AND FREEZING— ANDJl'S, LO\ELOCK and S^rITH 127 



stopped beating at +3° C. The hamster was then immersed in a bath of propylene 

 gl}col kept at —5° C. in a dee]) freeze cabinet. The body was covered with blotting 

 paper sodden witli tlie fluid at this temperature, and in this way its trunk and limbs 

 were weighted down and immersed completely while the mouth and nostrils were 

 kept above iluid level. Within 10 minutes the deep body temperature reached 

 — 0.6° C. as shown on the graph, and then levelled off dropping almost impercep- 

 tibly during the course of the next hour while the hamster froze progressivelv. 

 After freezing in this way for one hour the animal was so stiff that it could be 

 placed on a rack supported only at the head and tail and would, in addition, u])hold 

 its own body weight as shown l)y placing a 100 g. weight on the abdomen. It felt 

 woodlike to the touch and solid when knocked against the bench top. 



The frozen hamster was rewarmed by deep and rapid heating of the whole body. 

 This was done by means of a simple diathermy apparatus which had been built by 

 Dr. Lovelock. The animal was placed between the diathermy electrodes and the 

 high tension was switched on. Artificial respiration was given. The colonic tempera- 

 ture rose by about 1.0° to 2° C. per minute until it reached -1-10° C. Diathermy 

 was then stopped and the animal removed from the apparatus. Its heart was beating 

 steadily. Soon normal breathing was resumed and artificial respiration discontinued. 

 The nose, tongue, lips and paws which were deathly pale had become a rosy pink. 

 When respiration was regular the animal was washed in cold water to get rid of the 

 propylene glycol which was rather sticky. It was dried, and almost immediately 

 started to shiver. In this way it rewarmed itself and no further external heating was 

 needed. The hamster differs from the rat which does not shiver or rewarm spon- 

 taneously and requires to be heated artificially until its body temperature reaches 

 the normal level. Even after that the rat needs to be kept in a warm place for 

 several days. Within 40 minutes of being frozen stiff the hamster recovered mus- 

 cular activity. The animal which had been filmed during freezing and resuscitation 

 was by this time making vigorous efforts to turn itself over and finally, after a 

 minute or two, it succeeded. Thereafter it recovered rapidly and was seen one hour 

 later back in its cage, showing all the normal activity, including biting. 



The same animal was photographed again eight weeks later. It was in very good 

 health and showed no ill-effects. The only sign of damage due to freezing was loss 

 of the pinnae of the ears wdiich had become frostbitten because they had been 

 knocked and bent when frozen stiff. Other parts of the surface of the body and 

 extremities which had not been traumatized showed no signs of damage although 

 abundant ice had been present in all the superficial tissues. 



When cooled by the method shown, 75 per cent of hamsters became frozen. The 

 other 25 per cent, treated in exactly the same way, 1)ecame supercooled and the 

 deep body temperature fell below zero, in some animals reaching — 5° C. or below. 

 In supercooled animals no ice formed anywhere in the body. They were much 

 colder than the frozen animals but they remained soft and flabby and collapsed 

 unless the whole trunk was supported. This was illustrated in the film by putting a 

 supercooled hamster with a colonic temperature of —5.3° C. on the rack which sup- 

 ported it only at the head and tail. The animal promptly collapsed in a heap. It was 

 then rewarmed with diathermy by exactly the same technique illustrated for the 

 frozen animal. Artificial respiration was given as before. The heart rapidly resumed 



