EQUALIZATION OF THE ANIMAL TEMPERATURE. 433 



ditions, there is more or less loss of heat by evaporation from 

 the general surface, and when the surrounding atmosphere is 

 very cold, it becomes desirable to reduce this loss to the mini- 

 mum. This is done by appropriate clothing, which must 

 certainly be regarded as a physiological necessity. The 

 proper kind of clothing, the conducting power of different 

 materials, their porosity, etc., form important questions in 

 practical hygiene, and their full discussion belongs to special 

 treatises. Clothing protects from excessive heat as well 

 as cold. Thin, porous articles moderate the heat of the 

 sun, equalize evaporation, and afford great protection in 

 hot climates. In excessive cold, clothing is of the greatest 

 importance in preventing the escape of heat from the body. 

 When the body is not exposed to currents of air, the gar- 

 ments are chiefly useful as non-conductors, imprisoning many 

 layers of air, warmed by contact with the person. It is fur- 

 ther very important to protect the body from the wind, 

 which increases so greatly the loss of heat by evaporation. 

 It is wonderful, however, how intense a cold may be resisted 

 by healthy men under proper conditions of alimentation and 

 exercise and with the protection of appropriate clothing, as 

 in Arctic explorations, when the thermometer has for days 

 ranged from 60 to 70 Fahr. 1 



When from any cause there is a tendency to undue ele- 

 vation of the heat of the body, cutaneous transpiration is 

 increased, and the temperature is kept at the proper stand- 

 ard. We have already considered this question in treating 

 of the action of the skin, and have noted facts showing that 

 men can work when exposed to a heat much higher than 

 that of the body itself. The amount of vapor that is lost 

 lender these conditions is sometimes enormous, amounting to 

 from two to four pounds in an hour. 2 We have often noted a 

 loss of between two and three pounds after exposure for less 



1 HAYES, An Arctic Boat-Journey, Boston, 1860, pp. 257, 259, and American 

 Journal of the Medical Sciences, Philadelphia, 1859, Xew Series, vol. xxxviii., 

 p. 114, et seq. 2 See page 140. 



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