FRESH AIR AND EFFICIENCY 283 



impurities acting through the lungs, but to physical 

 changes which act through the skin. 



In order to explain the effects of this altered physi- 

 cal state of the atmosphere upon human beings it is 

 necessary to recall a few physiological and physical 

 facts. The heat-regulating mechanism of the human 

 body is a provision of essential importance to health 

 and life, and slight disturbances of it may produce 

 marked effects. If the equilibrium between our heat 

 production and our heat loss is disturbed, heat reten- 

 tion may ensue and symptoms develop that are closely 

 akin to those brought about by foul-air conditions; 

 and it is in a high degree probable that foul air acts 

 by inducing heat retention, which is responsible for 

 chemical changes in the tissues resulting in toxins 

 which produce headache, fatigue, &c. Indeed, a 

 vicious circle is established, for heat retention itself 

 causes a rise in temperature, and this increases oxi- 

 dation processes which lead to the production of more 

 heat. 



How does foul air induce heat retention? When 

 a human being sits in a warm room with a still 

 atmosphere he parts with heat to keep his body cool 

 mainly by the evaporation of moisture through the 

 sweat glands of his skin ; for then there is relatively 

 little loss of heat by radiation, convection, and con- 

 duction. In evaporation heat is rendered latent, and 

 the necessary heat is abstracted from his body surface, 

 and thus nature has provided a powerful means of 

 rapidly cooling the body and of so maintaining the 

 body temperature at the normal at exposures to very 

 high temperatures, such as those of the hottest rooms 

 of Turkish baths. But it is obvious that this evapora- 

 tion which helps us to cope with the excessive heat 

 production from within and heat reception from with- 

 out, cannot operate properly if the air has little or no 



