TOLERANCE TO HEAT AND DEHYDRATION IN SEVERAL SPECIES OF MAMMALS

Abstract

Dog, cat, rabbit, guinea pig, rat, and mouse were exposed to hot dry atmospheres (33[degree] to 58 [degree]C). Rectal temps. increased markedly, and furnished the most reliable index to survival. Rectal temp. had a different median critical value for each spp., lying between 41.7[degree] and 43.4[degree]C. Heat stroke resulted from hyperthermia that injured unidentified regulatory tissues. Death was often delayed for periods of 2-26 hrs. after animals had been subjected to critical rectal temps. Evaporative cooling of the body through panting was limited in all but dog and cat, and hence low humidities were of little advantage. But in all spp., evaporation proceeded just as rapidly after considerable dehydration as it did in water balance. Dehydration concentrated the blood plasma and embarrassed the circulation, rendering the animal very sensitive to warm atmospheres; explosive rises of rectal temp. then developed. In dogs and cats at least, renewal of water content was effective in keeping the body temp. down. Animals allowed water ad libitum did not drink enough water to maintain their body wts. while they were in hot atmospheres. After they had been deprived of water, they subsequently drank less than enough to recover their body wts.