398 CLOTHING. 



also is not without influence upon the temperature. Thus, a cowering 

 position and drawing together of the head and the extremities help to 

 retain heat, while spreading of the extremities, erection of the hair, 

 ruffling of feathers, permit the escape of a greater amount of heat. 

 Landois found that in rabbits suspended in air with their extremities 

 spread out the rectal temperature declined from 39 C. to 37 C. in 

 the course of three hours. Exposure in heated or cooled rooms, ingestion 

 of hot or cold food and drink, hot or cold baths, exposure to a quiet 

 atmosphere or to air in active motion (fanning) are measures employed 

 by man for regulating the temperature at will. 



In the cooling of the body from its surface, radiation, conduction (also through 

 the air) and convection (as the layer of air in contact with the body is constantly 

 being displaced by the heat) take part in addition to evaporation. The radiating 

 power of the skin has been carefully studied by Eichhorst and Masje. It is in- 

 creased after irritation and friction of the skin, after muscular effort, and in still 

 greater degree up to three or four times the initial amount through the action 

 of cold air or after a cold bath. After marked abstraction of heat radiation be- 

 comes small, while it is increased during the febrile process and after the employ- 

 ment of antipyretics. The amount of heat radiated by a naked man from each 

 square centimeter of superficies is equal to o.ooi calory in the second. This would 

 make for the entire body, weighing 82 kilos, approximately 1,782,000 calories in 

 twenty-four hours. Stewart found the loss of heat through radiation for a clothed 

 man, weighing 70 kilos, 700,000 calories; for a man, weighing 82 kilos, 820,000 

 calories. In a clothed person the radiation, according to Rubner, with a weight 

 of 82 kilos and a superficies of 22,430 square centimeters, is 1,181,000 calories. 



In estimating the influence of climate upon the regulation of heat of the body 

 chief importance is to be attached to the rapidity of evaporation, which is pro- 

 portional to the square root of the velocity of the wind. 



CLOTHING. 



The effect of the clothing is yet to be taken into consideration. A warm 

 dress is an equivalent for food, for as the dress is intended to preserve the heat 

 of the body generated by the latter from the combustion of food, it may be stated 

 that the body has a direct income through the food, while by means of clothing 

 it protects itself against unnecessary expenditure. The clothing thus at room- 

 temperature saves 20 per cent. From this its importance in the heat-economy is 

 obvious. Summer-clothing weighs from 3 to 4 kilos and winter-clothing from 6 

 to 7 kilos. The radiation of heat from the body through a full suit of clothing 

 is only about one-third of that from the naked skin. At a low temperature this re- 

 duction in heat-radiation is greater than when the surrounding temperature is high. 



With respect to the usefulness of clothing the following considerations are to 

 be borne in mind: (i) Its conductivity. Those materials that are the poorest con- 

 ductors of heat keep the body the warmest. The following is a list of conductors 

 arranged successively from the poorest to the best: Hare-skin, down, beaver-skin, 

 raw silk, taffeta, sheep's wool, cotton, flax, twisted silk. (2) The radiating power. 

 Rough substances radiate heat more readily than smooth substances. The radi- 

 ating power is, however, equal for different colors. (3) The relation to the sun's 

 rays. Dark materials absorb more heat from the sun than light materials. (4) 

 The degree in which materials are hygroscopic is of great importance, that is 

 whether they are capable of taking up much moisture from the skin, and at the 

 same time yield this up gradually by evaporation, or the reverse. Wool of the 

 same weight takes up twice as much water as linen, but the latter permits its 

 more rapid evaporation. Wool upon the skin, therefore, less readily permits 

 accumulation of moisture and also the development of cold through rapid evapora- 

 tion, and therefore affords protection against catching cold. (5) The degree of 

 permeability for air ventilation is of importance with respect to clothing, but it 

 bears no relation to heat-conduction. Thus the application of a coat of varnish 

 to materials increases the heat-conduction, but destroys the ventilation. The perme- 

 ability depends apart from the thickness of the material upon the specific gravity 

 and the character of the thread. The following is a list of substances beginning 

 with the more permeable and passing to the less permeable: Flannel, buckskin, 



