126 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



hour the colonic temperature had dropped ahuost to the centigrade zero. Dr. Andjus 

 said that rats kept without l^reathing and heart beats for one hour could regularly 

 be reanimated by rewarming the heart with microwaves. 



Dr. Parkes explained that the idea of using microwaves for heating the heart 

 originated from Dr. Lovelock, and that the apparatus had been designed by him 

 and built with the colla1)oration of Mr. Perkins in the Instrument Division of the 

 Institute. He then introduced Dr. Lovelock who demonstrated his magnetron micro- 

 wave generator which pours forth a flood of very high frequency radio waves. 

 These radio waves can be projected in a narrow beam and are able to penetrate the 

 skin of an animal and warm up its inner organs. Neither heat radiations nor longer 

 radio waves share both of these properties. 



Dr. Andjus then showed how the chilled rat was arranged in the path of the 

 microwaves. The animal was placed under a wave-guide. The cardiac area was 

 heated preferentially because it was situated under an appropriate sized hole in the 

 wave-guide. The heart beat was thus re-established rapidly and before the extremi- 

 ties had become warmed. Artificial respiration was simultaneously administered by 

 intermittent insufflation of air into the lungs through a rubber tube applied to the 

 nostrils. An automatic air pump was used. After 15 minutes a regular cardiac 

 rhythm had been re-established, heating and artificial respiration were discontinued 

 and the animal took its first breath. The colonic temperature was still only 20° C. 

 Movements of the head and tongue could soon be elicited. Respiration rapidly 

 became regular as shown by kymographic tracings. The animal was then immersed 

 in a bath of water at 40° C. to warm it further. Within 30 minutes it had regained 

 muscular tone and the body temperature had reached approximately 30° C. The rat 

 was then removed from the bath, dried, and put into an incubator running at 28° 

 to 32° C. When placed on its back it turned over spontaneously. The animal was 

 seen again one hour later sitting up and apparently in good condition. Dr. Parkes 

 commented that Dr. Andjus had thus cleared the way for the second of the two 

 prolDlems previously mentioned, namely what would happen to an animal when the 

 body temperature fell below zero. For this part of the work the golden hamster was 

 selected because it had proved comparatively easy to handle in the range of body 

 temperatures above zero. Dr. Parkes then introduced Dr. Smith who was at work 

 in the laboratory. She showed a golden hamster in its cage, and explained that this 

 rodent differs from the rat in being a potential hibernator. The experiments were, 

 however, being carried on during the summer and the hamster was full}- acti\e. The 

 hamsters were cooled by a method similar to that used for the rat. An animal was 

 enclosed in a jar which was packed into ice. During the two hours which followed 

 the deep body temperature fell by 20° C. to 18° C. The animal was then uncon- 

 scious, and was transferred to a dish of crushed ice and surrounded by ice-cold 

 water so that only its nose protruded. The body temperature fell still further but. 

 unlike the rat, the hamster continued to breathe until it had cooled down to approxi- 

 mately + 5° C. which is the lowest temperature usually reached in natural hiberna- 

 tion. During natural hibernation breathing and heart beats are slowed but never stop 

 completely. The hamster was shown taking its last breath at the time when the 

 colonic temperature was at +4.5° C. The deep body temperature was recorded 

 continuously on a graph from a thermocouple inserted into the colon. The heart 



