312 ANIMAL HEAT. 



have been in many instances accurately determined. According to the 

 experiments of Sachs, the limits of germination for wheat and barley 

 are between 5 and 38, and for Indian corn between 9 and 42. The 

 irritability and periodic movements of the sensitive-plant do not show 

 themselves unless the temperature of the surrounding air be above 15. 

 In air at 48 to 50, on the other hand, the leaflets become rigid in a 

 few moments, though they may afterward recover if the temperature be 

 moderated; while a heat of 52 permanently destroys their vitality. 

 Thus no vegetative function can come into activity, unless the tempera-, 

 ture of the plant reaches a certain degree above the freezing point ; and 

 it ceases, furthermore, if the temperature rise above another determinate 

 degree, which cannot for any considerable time exceed 50. Within 

 these two limits, also, every vegetable function has a special tempera- 

 ture at which it is most active; diminishing in intensity both above 

 and below this point. 



Observation shows that the same is true of the animal functions. 

 Each species of animal has a definite bodily temperature, and this tem- 

 perature cannot be raised or lowered beyond certain limits without 

 arresting the phenomena of life. Mammalians, whose normal tempera- 

 ture 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 soon 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 themselves are fatally affected when their internal temperature is 

 raised to 48 or 50. In every case the vital functions are seriously 

 disturbed by a very moderate change in the actual temperature of the 

 bodily organs ; and in the mammalians, as a general rule, death follows 

 when this change amounts to an elevation of 6 or 7, or to a depres- 

 sion of 20. 



In the human subject, 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 

 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 the temperature rises to 42.5 or 43 a fatal result is 

 almost inevitable. 1 



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

 warm-blooded animal be exposed to cold in such a way as to abstract 

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

 and continuous depression of the vital functions. After a short period 

 of pain in the more exposed and sensitive parts, the skin becomes 

 insensible, the muscles lose their contractile energy, the movements of 

 respiration diminish in frequency, and the nervous system becomes more 

 and more inactive. In the human subject a marked sluggishness of 



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



