REGULATION BY EVAPORATION. 851 
Thus it happens that the animal can diminish or increase its loss of heat 
according to its nerds. 
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 3 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 
Farther, 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 moist, 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 
Schuster, Arch. f. Hyg., Mlinchen 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 Virchow's 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. lxv. pp. Ill and 484. 
