ANIMAL HEAT. 269 



ature of the plant reaches a certain degree above freezing ; and it ceases 

 at another determinate temperature, which cannot for any considerable 

 time exceed 50. Within these two limits every vegetable function has 

 a special temperature at which it is most active ; diminishing in inten- 

 sity both above and below this point. 



The same is true of the animal functions. Each species of animal 

 has a definite bodily temperature, which cannot be raised or lowered 

 beyond certain limits without injury. Mammalians, whose normal 

 temperature is from 37 to 40, become insensible and soon die, when 

 cooled down to 18 or 20, which is the natural standard for reptiles and 

 fish ; while a frog is killed by being kept in water at 38. On the other 

 hand, mammalians die when their blood and internal organs are heated 

 up to 45, which is precisely the normal temperature of birds; and 

 birds are fatally affected when their temperature is raised to 48 or 50. 

 In every case the vital functions are seriously disturbed by a very mod- 

 erate change in the temperature of the bodily organs ; and in the mam- 

 malians, as a rule, death follows when this change amounts to an 

 elevation of 6 or 7, or to a depression of 20. 



In man, in febrile affections, the rise of temperature, as measured in 

 the axilla, yields a very accurate criterion of the gravity of the disease. 

 An increase of this temperature from 36.6 to 37.5 or 38 C. indicates 

 a mild form of the malady ; but an increase to 40 or 40.5 shows that 

 the attack is severe. Above 40.5 it is a symptom of great danger; 

 and when it rises to 42.5 or 43 a fatal result is almost inevitable.* 



Effects of Lowering the Temperature of the Animal Body. If a 

 warm-blooded animal or man be exposed to cold in such a way that the 

 internal heat is abstracted faster than it can be produced, the effect is a 

 general depression of the vital functions. After a short period of pain 

 in the more exposed parts, the skin becomes insensible, the muscles 

 lose their energy, the movements of respiration diminish in frequency, 

 and the nervous system becomes inactive. In man a marked sluggish- 

 ness of mind, and a disposition to sleep have been observed as among 

 the symptoms of continued exposure to unusually low temperatures. 



The general effects of a low temperature result from its combined 

 influence on all the organs and tissues. According to Bernard, if 

 a rabbit or guinea-pig be subjected to continuous abstraction of heat, 

 the temperature of the animal, as taken in the rectum, gradually falls 

 from 38 to 30, 25, 20, and 18. When the depression has reached 

 this point, there is general insensibility and paralysis, with feeble and 

 infrequent respiration. The heat-producing power is also lost, so that 

 if the animal be withdrawn from the apparatus, and kept in the air at 

 10 or 12, its temperature, nevertheless, continues to diminish, and 

 death takes place after a short time. 



But when in this condition, although most of the vital actions are 

 suspended, and the animal has lost the power of maintaining his own 



Flint, Principles and Practice of Medicine. Philadelphia, 1868, p. 109. 



