THE EXTERNAL ENVIRONMENT 239 



the defence of the organism against heat. The rejected water 

 evaporates on the surface of the skin at the same time absorbing 

 a quantity of heat. 



Sudation is therefore a factor in the equilibrium of the organism 

 which obeys, like all the others, the nervous co-ordination. It 

 would be very serious if it were not so. for sweat is a toxic waste, 

 and is produced during fatigue ( 158). The poisons which it 

 eliminates in twenty-four hours would be sufficient to endanger 

 an adult subject, f 1 ) Poisoning sometimes takes place in a hot, 

 humid atmosphere if the sweat has not been able to leave the 

 body.f 2 ) Therefore the necessity for the regulation or of the 

 emission of water vapour in a manner adapted to biological ends 

 will be understood. 



In an environment at a temperature of 20 C. a male adult 

 eliminates about 900 grammes of water in the state of repose ; 

 3,000 grammes in an average amount of work of 200,000 kilo- 

 grammes ; in the case of exceptionally hard work 7 to 8 kilo- 

 grammes of water. Walking in the desert causes an enormous 

 sudation, often disastrous to the health. The evaporation of these 

 considerable quantities of water corresponds to a great expend- 

 iture of heat. 



Any circumstances which impede perspiration are dangerous ; 

 such as the humidity of the rooms of cotton mills (on an average 

 85% at a temperature of U3 C.) ( 3 ) or dust which obstructs the 

 pores of the skin. One suffers from damp heat,( 4 ) says Rubner, 

 because of the inability to evaporate sufficiently. One suffers 

 from damp cold, because it causes too much loss of heat.( 5 ) 



It is desirable to reduce humidity by adequate ventilation ; 

 because, on the one hand, sudation will then take place normally, 

 and on the other, the heat will be more bearable in a relatively 

 dry environment, as damp air retains the heat longer. ( 6 ) 



A dry state of the atmosphere is favourable to work, especi- 

 ally at an average temperature of 15-16C ; it is only in very 

 particular cases that extreme dryness is accompanied by trouble 



( x ) Arloing (Journ. de Physiol., 1899, pp. 249, 268). 



( 2 ) Haldane (Revue Scientifique, 8th Oct., 1910). 



( 3 ) P. Boulin (Ibid., 8th April, 1911, p. 430). 



(*') In various countries, as at Buenos-Ayres, the moisture combined 

 with a temperature of 39 and 40, caused numerous deaths in 1900. 

 (Grandis and Mainini, Arch. Ital. Biol., vol. xxxvii., No. 281, 1901). 



( 6 ) Rubner (Arch. f. Hygiene, vol. xxxviii., p. 120, 1900). 



( c ) Hoorweg, Haga (Journal de Physique, 1877). 



