make a study of these acute manifestations in the hope of devising a rational, and if 

 possible, effective form of therapy. The mortality rate in human victims of hyper- 

 thermia or heat stroke is very high; effective therapy is an acute necessity : in War 

 perhaps even more than in Peace. 



Our experimental animals were rabbits; they cannot sweat; the rabbit attempts 

 to cool its body — in a hot environment — by breathing quickly over the moist red 

 tongue and lips. In our initial experiments the emphasis was on respiration; after 

 exposure to the sun (138°F) the rectal temperature of an adult healthy rabbit reached 

 110. 0°F with respiration rate 125 per minute, carbon dioxide exhaled 230ml/sq.m./ 

 min. and volume of expired air 2100ml/min. Ice was then applied to the whole of 

 the fur and the rectal temperature dropped to 104. 0°F, the respirations, carbon di- 

 oxide and volume falling to 120, 190, and 1700, but rising again to 140, 250, and 

 2700 at the end of the experiment. The animal made a complete recovery but gave 

 birth to two stillborn young a few hours later. As a result of a number of experi- 

 ments we found that if the respiratory activities were stimulated by a rising body 

 temperature, the animal tended to recover. At the peak of body temperature some 

 animals collapsed; one such with a rectal temperature of 112.2°F stopped breathing: 

 the carbon dioxide in the exhalations had increased as the body temperature rose, 

 but there was no compensatory increase in ventilation; the respiratory centre in the 

 brain appeared to have become relatively insensitive to increases in the carbon di- 

 oxide tension in the blood. Cyanosis was not observed in this animal, so the brain 

 cells may have been depressed by some other factor, mere heat or reduction of the 

 blood pH. This collapsed animal responded to ice applied to its fur, and behaved 

 normally for some hours, after its body temperature had been reduced, but late in the 

 evening he was discovered with a subnormal rectal temperature, pale ears, inaudible 

 heart beats, sighing respirations and very weak. The respirations had dropped to 60 

 per minute. This animal was painlessly destroyed to avoid further suffering and 

 portions of the body tissues were preserved for histological examination. 



Another rabbit showed respiratory stimulation in the early stages of the experi- 

 ment, with respiratory depression near the peak of the body temperature (108.0°F) but 

 the respirations quickened again after cooling treatment. The ventilation increased 

 in response to the increased concentration of carbon dioxide in the exhalations — 

 and presumably, increased carbon dioxide tension in the blood — an indication that 

 the respiratory centre in the brain was sensitive and reacting normally; a good sign. 

 Yet another rabbit suffered a rise in rectal temperature to 113-6°F rather quickly and 

 died suddenly at the peak; before the crisis he had responded well. Still another 

 rabbit was taken up to a peak temperature (rectal) of 111.1°F respiratory stimulation 

 was shown until the crisis was reached, when there was a short period of depres- 

 sion, followed by further stimulation on cooling. This rabbit appeared to have been 

 successfully treated, and made a good recovery, which, however, proved only tem- 

 porary. Having spent the night in comfortable cool surroundings, he was found dead 

 next morning. 



Provided the rectal temperature did not exceed lethal levels, the cardio -vas- 

 cular system seemed to adjust itself to the high body temperature during the acute 

 phases of heating up and cooling down. If the cooling process was delayed or omit- 



189 



