SUPERCOOLING AND FREEZING— ANDJUS, LOVELOCK and SMITH 135 



the total barometric pressure with a vacuum pump, or by absorbing the expired 

 carbon dioxide in a container of appropriate size). It is also possible to use hyper- 

 capnia alone for inducing hypothermia (l)y enclosing the animal in a vessel filled 

 with pure oxygen), but we have found that under these conditions and by the time 

 the body temperature has fallen below 20° C. the accumulation of carbon dioxide 

 reaches values which are very close to the lethal concentrations. Many of our rats 

 cooled by this technique succumbed even when returned to normal air. It is to be 

 noted that carljon dioxide is much more lethal for the animal in hypothermia 

 (Giaja and Markovic, 1953). The closed container technique, with ordinary air and 

 with no carbon dioxide removal, remains the simplest and safest method in-so-far as 

 the rat is concerned. 



Although the closed vessel remains our technique of preference for rats and 

 other small laboratory animals, it is less convenient for such animals as the monkey 

 and the dog where the size and surface ratio becomes an important limiting factor. 

 The larger the animal, the slower is the rate of cooling and, consequently, the 

 greater the danger of asphyxiation occurring before low temperatures can be 

 reached. 



Despite the size factor, we used the closed vessel technique in our experiments 

 with monkeys as shown in the film. The animal is enclosed in a large perspex box 

 and immediately anesthetized by introducing pure carbon dioxide into the box. The 

 box is then placed in a refrigerator and refilled with nitrogen containing 7 per cent 

 oxygen. From then on, the expired carbon dioxide is allowed to accumulate. 



It is obvious, however, that by such a technique (cooling in air at 0° C.) the 

 rate of cooling is always much slower than when cooling is achieved by immersion 

 in icy water. It may be mentioned that carbon dioxide can be very useful for the 

 suppression of shivering during cooling by immersion. We are now cooling dogs 

 down to 15° C. by immersion, using only carbon dioxide and intravenous alcohol 

 for narcosis and suppression of shivering. 



Final cooling to 0° C, and supercooling. Once the body temperature is low- 

 ered to 15-20° C, the animal is removed from the vessel and further cooling is 

 achieved by covering the animal with crushed ice. The animal is cooled to 0? C, and 

 then supercooled by immersion in a propylene glycol or glycerol bath kept at —6° C. 

 No artificial respiration or circulation is applied in the last stage of cooling because 

 respiratory and cardiac arrest have already occurred (see fig. 4). To date, the lowest 

 temperature from which we have resuscitated animals has been about — 5° C. 



RESUSCITATION BY LOCAL HEATING OE THE CARDIAC AREA 



In 1951 we reported a technique for resuscitation of animals cooled to body tem- 

 peratures around 0° ( Andjus, 1951). Applying this technique, we have succeeded 

 in reanimating adult non-hibernating mammals cooled to body temperatures reach- 

 ing even a few degrees below the freezing point (Andjus, 1955). 



Our experiments proved that deeply cooled animals with a cardiac arrest lasting 

 up to almost two hours and body temperatures reaching about — 5° C. can be re- 

 suscitated by localized external application of heat to the cardiac area. This strategy 

 re-established the adequate circulation of blood ahead of the tissue requirements for 



