MILAN 



and specific to the part of the body which is repeatedly stimulated. 

 "General habituation" might be explained asachangein the psycho- 

 logical "set" of the subject relevant to the conditions of experimen- 

 tation so that he is no longer apprehensive, either consciously or 

 unconsciously, at the time of the test. 



These two types of habituation can develop simultaneously. 

 Both depend upon a change in the manner in which the central ner- 

 vous system interprets its afferent impulses. Both involve a pro- 

 gressive diminution in response to a repeated stimulus. Where the 

 stimulus is the application of severe cold, specific and general 

 habituation are manifested by reduced pain sensation and by 

 reduced vasoconstrictor activity, respectively. 



Both types of habituation as well as a local vascular adapta- 

 tion were demonstrated in experiments done at the Arctic Aero- 

 medical Laboratory (Eagan, 1960a*, 1960b**, 1961***). In all 

 experiments, regimens of unilateral cold exposure ("test" side 

 only) followed by simultaneous bilateral comparison ("test" vs. 

 "control') were used in investigations of local tissue cold adapta- 

 tion in the fingers of man. A summary of these experiments follows. 



Chronic hand cooling of moderate intensity (12 hours per 

 day with finger temperature between 10 C and 15 C for ten 



*Eagan, C. J. 1960a. Topical adaptations to cold in the extremities. Proc. 

 XI Alaskan Sci. Conf. pp. 184-185. 



♦♦Eagan, C. J. 1960b. Unilateral cold adaptation to recurrent ice water immer- 

 sion. Physiologist, 3(3) :51. 



♦♦♦Eagan, C. J. 1961. Habituation to recurrent ice water immersion of the finger. 

 Physiologist, 4(3) :3l. 



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