HUMAN EACIAL BESPONSES 



days) resulted in a less intense initial vasoconstriction, less varia- 

 bility in digital blood flow and a 17% greater average heat loss, dur- 

 ing a 30-minute period of ice- water immersion. Fingers of the test 

 hand cooled more slowly than the control fingers during exposure to 

 cold air. Pain sensation tended to be less for the test hand, espe- 

 cially for the fingers; this type of cold adaptation was termed "spe- 

 cific habituation" — specific to the cold stimulus and to the part of 

 the body stimulated. 



Recurrent f inge r cooling of severe intensity (six 5- minute ice- 

 water immersions per day for 17 days) caused a marked, specific 

 habituation to cold pain. There was no essential difference between 

 the vascular reactions of test and control fingers when they were 

 tested in ice water. Prolonged recurrent finger cooling (six 10- 

 minute ice-water immersions per day for 125 days) confirmed the 

 finding that specific habituation to pain could develop in the absence 

 of local vascular cold adaptation. However, the subjects did show 

 higher finger temperatures (test and control fingers alike) in ice 

 water, compared with other subjects being tested forthe first time. 

 This was concluded to be a "general habituation" to the conditions 

 of the experiment which resulted in less vasoconstrictor outflow to 

 fingers in ice water. 



It is considered that the results on general habituation are 

 highly relevant to what has been discussed above by Milan. Many 

 racial differences in the responses of the extremities to cooling 

 have been attributed either explicitly or implicitly to localized 

 vascular adaptations. These differences may on the contrary be 

 related to the degree of habituation to cold exposure and the 

 experimental conditions. Further, the energy state of the subject 

 at the time of the test is not always taken into account. 



A comparison of the responses to finger cooling in four groups 

 of subjects is demonstrated in Table III and Figure 4. 



The habituated group consisted of the six USAF airmen who 

 had each immersed one middle finger in ice water 750 times over the 



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