232 THE HUMAN MOTOR 



functions, but they modify appreciably the expenditure of energy, 

 and reduce the amount of work. A low temperature raises the 

 expenditure of energy, or the living ration, to a very high value ; 

 a high temperature limits the production of work. 



The r61e of climate is defined by what has been said above, 

 apart from other characteristics the hygrorretric state, the 

 altitude, and the latitude. Arctic climates, where the cold reaches 

 50, and sometimes even - 80 C., have a curious effect on 

 the nutritive exchanges. Then, when the organism has to feed 

 well and breathe deeply, the action of the polar temperature 

 retards the rhythm of the respiration and disturbs slightly the 

 expiration of the gases (Nansen, Amundsen, etc.). In spite of 

 this, by the protection of furs, man contrives to keep a constant 

 central temperature. 



When, owing to insufficient protection, or defective organic 

 resistance (alcoholism) the organism cools internally, life is in 

 danger. If the internal temperature reaches 32 C. a fall of 

 5-5 C., death is practically certain. In the same way, if the 

 central temperature rises from 37-50 to 43 or 44 C., there is also 

 danger of death. Poisoning often leads to hypothermia. 



Under strictly physiological conditions, with a normal subject, 

 and for the usual range: of temperature, the action of the latter 

 is balanced by the nutritive exchanges, and is complicated or 

 corrected by clothes, the humidity of the air, and the speed 01 

 the atmospheric currents ; this last factor affecting tht. convec- 

 tion and pressure exerted on the muscles. 



170. Influence of Clothes. The human skin and hair protect 

 the central temperature inefficiently. Therefore man protects 

 himself artificially by means of clothes. It is obvious that the 

 protective power of the latter depends on the nature and the 

 thickness of the material, that is to say, on its conductivity. We 

 know that the conductivity of the human skin is 0-0006, i.e., this 

 is the quantity of heat in small calories that will pass per square 

 centimetre through a thickness of 1 cm. with a temperature 

 difference between the two surfaces of 1 C. It is recognised 

 that the conductivity of the skin decreases in glacial regions, 

 because of the fatty tissue which lines it. 



Various measurements have been made of the co-efficient of 

 conductivity of various materials. The most complete and 

 correct are those of Rubner, f 1 ) who used several calorimeters 

 of different sizes. Rubner showed, first of all, that the best 

 heat insulator is the air ; its co-efficient of conductivity being 

 0000532. If it were possible to surround 'the body with a layer 

 of air of a suitable thickness it would be better protected than by 

 any garment of equal thickness. 



(*) Max Rubner (Arch.f. Hygiene, vol. xxiv., p. 265 sqq. t 1895). 



