128 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



beating and within 10 minutes was beating steadily so that the fur over the prae- 

 cordium pulsated visibly. After 15 minutes the animal had resumed natural breath- 

 ing. Within 30 minutes it had turned over and was shivering vigorously. Within 

 one hour it was moving round actively, none the worse for its experiences, and 

 actually looking for food. It recovered completely and showed no ill effects either 

 within a few hours or many months after cooling to —5.3° C. 



Dr. Smith said that the work on rats and hamsters shown in this film was only a 

 beginning and was being extended to larger animals. Experiments on monkeys sug- 

 gested that there were no fundamentally different problems and that there should 

 be no insuperable difficulties either in cooling or in resuscitation. For instance. Dr. 

 Andjus was shown cooling a monkey in a closed vessel in the refrigerator. After 

 it had been narcotised with cold it was packed into crushed ice with only the nose 

 protruding. The deep body temperature fell to -f5° C, and breathing was arrested 

 for one hour. Dr. Andjus then revived the animal by means of diathermy and 

 artificial respiration. Dr. Smith thought that this work might have important bear- 

 ings on surgical anesthesia, particularly in facilitating operations on the heart by 

 allowing animals to be cooled to lower temperatures than were hitherto considered 

 safe and thereby prolonging the period during which the heart could be excluded 

 from the circulation and subjected to operations. 



In order to keep animals in a state of suspended animation for periods longer 

 than a few hours it would, on the other hand, undoubtedly be necessary to cool them 

 to much lower temperatures in order to reach a state of biochemical and physical 

 stability. Research along these lines had already begun at the National Institute for 

 Medical Research. 



ADDENDUM : 

 FORMATION OF ICE IN TISSUES 



Furnished by A. U. Smith 



Dr. Lovelock and Dr. Smith have examined the distribution of ice within the 

 body and have determined the amount of ice formed in the various tissues and 

 individual organs as well as in the whole body of hamsters frozen for varying 

 periods at —5° C. In hamsters frozen for 60 minutes as much as 90 per cent of the 

 water in the skin, 60 per cent of the water in the brain, and 40 to 50 per cent of 

 the total body water was often frozen. Nevertheless, animals frozen to this extent 

 could be completely resuscitated. The proportion of early deaths and incomplete 

 recoveries increased rapidly when the duration of freezing was prolonged so that 

 no animal frozen for more than 70 minutes survived more than a few days. Breath- 

 ing and heart beat were temporarily resumed in animals frozen for 170 minutes, but 

 there was no sign of life in those rewarmed after freezing for three hours or more. 



These results, as well as the effects of foetal development of freezing pregnant 

 hamsters, will be reported in detail elsewhere (Smith, 1955 a & b; Lovelock and 

 Smith, 1955). Hamsters resuscitated after freezing progressively at —5° C. do not 

 necessarily become frostbitten in spite of the presence of abundant ice within the 

 superficial tissues. Frostbite can, however, be induced by several methods which 

 include bending the frozen extremities, and applying solid carbon dioxide at 

 -79° C. to the frozen part (Smith, 1954). 



