REGULATION OF THE ANIMAL TEMPERATURE. 313 



mind and a disposition to sleep have been observed as among the symp- 

 toms of long continued and dangerous exposure to unusually low tem- 

 peratures. 



The local effects of cold upon the nervous tissues in man have been 

 shown by the experiments of Dr. Weir Mitchell, 1 in chilling the ulnar 

 nerve at the elbow by the application of a freezing mixture. This at 

 first produces pain in the hand, subsequently followed by loss of sensi- 

 bility and motive power in the parts corresponding with the distribu- 

 tion of the nerve. 



The general effects of a lowered temperature result from its combined 

 influence upon all the separate organs and tissues. According to the 

 observations of Bernard, if the body of a rabbit or a guinea-pig be sur- 

 rounded by snow or ice so as to prevent spontaneous motion and to 

 cause a continuous abstraction of heat, the temperature, as taken in 

 the rectum, gradually falls from 38 to 30, 25, 20, and 18. When 

 the depression of the bodily temperature has reached this point, the 

 animal is insensible and paralyzed, and the respiration feeble and infre- 

 quent. The heat-producing power is also lost, so that if the animal be 

 withdrawn from the cooling mixture and kept in the air at 10 or 12, 

 the temperature of the body continues steadily to diminish, and death 

 takes place after a short time. 



But when in this condition of depression and insensibility, although 

 most of the vital actions are suspended, and the animal has lost the 

 power of maintaining his own temperature, if he be supplied with arti- 

 ficial warmth up to a certain point, he may regain his vitality, and the 

 processes of life be again put in operation. The respiration, which 

 was reduced to a minimum by the continued action of cold, becomes 

 increased in rapidity as the body is artificially warmed, and the func- 

 tions of the nervous and muscular systems are also finally restored. 



A striking example of the temporary suspension of the bodily func- 

 tions by cold is presented by the hibernating animals, as marmots and 

 some species of squirrels, which pass into a condition of torpor during 

 the winter, becoming insensible, unconscious, and immovable, while 

 at the same time respiration is nearly imperceptible, and the bodily 

 temperature sinks to 10, 8, or even 2. Life, however, is not abol- 

 ished but only held in abeyance ; and with the return of spring all the 

 functions resume their activity. A hibernating animal is accordingly 

 somewhat in the condition of a seed, which remains in the ground over 

 winter, with its vitality dormant, but ready to come into action when 

 supplied with the requisite degree of warmth. 



Effects of Elevating the Temperature of the Animal Body. If the 

 temperature of the body, in a living animal, be artificially raised some 

 degrees above the normal standard, the effects are quite different from 

 those produced by cold. In the experiments of Bernard, the animals, 

 both birds and mammalians, were inclosed in a cage with heated air ; 



1 Injuries of Nerves and their Consequences. Philadelphia, 1872, p. 59. 

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