REGULATION BY E VAPORATION. 851 



Thus it happens that the animal can diminish or increase its loss of heat 

 according to its needs. 



Other conditions, however, play an important part in this regula- 

 tion. In the case of man the epidermis and the subcutaneous fat are 

 bad conductors ; and, by means of clothing, 1 the greater part of the body 

 is so protected that it is in contact not with the external air, but with 

 a fairly stationary layer of air, with a temperature from 24 to 30. In 

 other warm-blooded animals protection is afforded by the fur or feathers, 

 which prevent loss of heat not only by their thickness and slight power 

 of conduction, but by enclosing strata of more or less stationary warm 

 air. The more stationary the air the less the loss of heat, for the body 

 becomes surrounded with a layer of air having a temperature inter- 

 mediate between that of the body and of the atmosphere. Thus, during 

 Parry's expedition to the Polar seas, the sailors found that they could 

 better bear a cold which would freeze mercury ( 40), when the air 

 was perfectly calm, than a temperature of 12'2 when there was a 

 wind. 2 The men of Franklin's expedition had the same experience. 3 

 Further, the capacity of dry air to take up heat is much less than that 

 of moist air ; hence it happens that in dry, calm air several degrees below 

 zero, much less sensation of cold may be felt than in moist air with a 

 temperature a few degrees above the freezing point. 



In the whale, seal, and walrus, the thick epidermis and the large 

 amount of subcutaneous fat so perfectly prevent excessive loss of heat, 

 that their high temperature can be maintained in the Arctic seas. 

 Greyhounds, on the other hand, feel even moderately cold weather very 

 quickly, for, as the result of selective breeding, they have little fur and 

 hardly any subcutaneous fat. 4 Vierordt 5 calculated that an adult man 

 lost 1,791,820 calories, or 73 per cent, of the total loss of heat, by 

 radiation and conduction from the skin in twenty-four hours. Masje, 6 

 from experiments made with a thermoscope, constructed on the principle 

 of Langley's bolometer, concludes that the heat lost by radiation from 

 the skin of an adult man, weighing 82 kilos, and with a surface of 

 20,000 square cms., is 1,700,000 calories in twenty-four hours. Similar 

 experiments have also been made by Stewart. 7 



Evaporation. Benjamin Franklin 8 observed, during the hot weather 

 at Philadelphia in 1750, that his temperature remained normal, although 

 the external temperature was 37'8 in the shade. He attributed this 

 result to the cooling effect of the evaporation of sweat. This was proved 

 by Blagden 9 during his experiments upon the effect of extreme heat on 

 the body. When the air was rnoist, the temperature of the body rose ; 

 whereas in dry air, heated to 126, the temperature did not rise above 

 the normal. Into the heated room two jars of water were brought, and 

 a layer of oil was placed on the surface of the water in one, with the 



1 Schuster, Arch. f. Hyy., Munchen u. Leipzig, 1888, Bd. viii. S. 1; Rubner, ibid., 

 1890, Bd. xi. S. 255. 



2 "Journal of a Second Voyage to the Arctic Regions." 



3 Franklin, " Journey to the Polar Sea, 1819-1822," 2nd edition, vol. ii. pp. 27, 28. See 

 also Ross, "Narrative of a Second Voyage in Search of a North- West Passage," London, 

 1835, pp. 285, 287, 297. 



4 Bergmann, " Gottinger Studien," 1847, Abth. 1, S. 595. 



5 " Grundriss der Physiol. des Menschen." 



6 Virclwufs Archiv, 1887, Bd. cvii. S. 17, 267. 



7 Stud. Physiol. Lab. Owens Coll., Manchester, 1891, vol. i. p. 100. 



8 "Experiments and Observations on Electricity," London, 1769, p. 366. 



9 Blagden, Phil. Trans., London, 1775, vol. Ixv. pp. Ill and 484. 



