314 ANIMAL HEAT. 



the air being sometimes dry and sometimes loaded with moisture, but 

 renewed by due ventilation. The primary effects were increased fre- 

 quencjr of respiration and an appearance of discomfort and agitation ; 

 and finally death took place usually with convulsive movements, some- 

 times accompanied by an audible cry. The fatal result was more rapidly 

 produced in birds than in mammalia. Thus, a rabbit placed in the cage 

 with dry air at 65, died in twenty minutes; and a bird, in air at the 

 same temperature, died in four minutes. This difference is no doubt 

 partly due to the greater activity of the circulation in birds, by which 

 external heat is more rapidly transferred to the internal organs ; since 

 the same observer found that of two rabbits, one living and one dead, 

 placed in the warm cage at 100, the internal temperature of the living 

 animal became sensibly raised sooner than that of the dead one. In a 

 medium of high temperature, therefore, a fatal amount of heat reaches 

 the internal organs more rapidly by means of the circulation than by 

 simple conduction through the solid tissues. 



After death from exposure to too warm an atmosphere, the internal 

 temperature is found to be 5 or 6 above the normal standard; the 

 heart is motionless ; both the muscles and the nerves are insensible to 

 the stimulus of galvanism ; and lastly, cadaveric rigidity is established 

 with unusual promptitude. In many instances the blood is found dark- 

 colored in the arterial as well as in the venous system ; but this is a 

 post-mortem change, since observation shows that the arterial blood 

 continues red so long as life lasts, while its oxygen disappears and its 

 color darkens with great rapidity after the stoppage of respiration. The 

 appearances indicate that an unnaturally high temperature produces 

 death by hastening, in an undue degree, the chemical changes taking 

 place in the tissues and fluids, in such a manner that their vitality is 

 rapidly exhausted and can no longer be maintained by the usual pro- 

 cesses of nutrition. 



Resistance of the Living Body to Low External Temperature. Since 

 an actual depression of the temperature of the body is followed by such 

 serious results, and as, in point of fact, its temperature is maintained in 

 health at the normal standard, notwithstanding exposure to varying 

 degrees of cold, it is evident that the living organism possesses the 

 power of increased production of internal heat, to compensate for the 

 greater loss without. In the experiments of Senator on the abstraction 

 of warmth, by confining dogs in close cages surrounded by a cold me- 

 dium, it was found that the total amount of heat produced by the ani- 

 mal was not increased. But in these cases the animals were placed 

 under conditions by which their natural movements were prevented, 

 and the results obtained were due to simple cooling of the body, with- 

 out the action of compensating causes. In the natural, unconfined con- 

 dition, the effect is different. It is a matter of common observation, 

 that the influence of moderate external cold, if not too long continued, 

 produces a sense of warmth and increased vigor, instead of depression. 

 The atmosphere of a winter's day, or a cold shower bath, acts as a 



