TEMPERATURE AND HUMIDITY 



69 



Normal Temperature— The normal temperature of man is the 

 resultant between the heat produced by the oxidation of foodstuffs 

 in the muscles, glands, and other organs and tissues of the body, 

 and the heat lost by warming the urine, faeces, and expired air, by 

 evaporation from the lungs and skin, and by radiation and con- 

 duction from the skin. In other words, the temperature of 

 the body is controlled both by chemical and by physical heat 

 regulation. 



1. Chemical Heat Regulation. — By this is meant regulation of the bodily 

 temperature by increased or diminished production of heat, which can be 

 brought about by alterations in metabolism. Diminished heat production 

 is, however, rare, being usually pathological, though it is possible that it 

 occurs more frequently in the Tropics than in the Temperate Zone, owing to 

 the lessened disposition for muscular or mental work. 



2. Physical Heat Regulation. — -The body temperature is usually regulated 

 by increasing or diminishing the loss caused by radiation, convection, and 

 evaporation. According to Hill, a man weighing 70 kilogrammes loses 77- 1 

 per cent, of his heat by radiation and convection and 22*9 per cent, by evapora- 

 tion. This regulation is brought about by the dilatation of the cutaneous 

 vessels bringing more blood to the skin and by the increased perspiration. 

 The loss of heat caused by radiation and convection depends upon — 



Clothing may, however, affect the loss of heat from the skin, for, as a rule, 

 it is composed of substances which are bad conductors of heat, and hence 

 the loss may, according to Rubner, be diminished no less than 47 per cent. 

 Wet clothing, on the other hand, is a good conductor, because of the water 

 in its interstices, and hence the danger of chills while wearing damp clothes. 

 This latter fact is well known to the old resident of the tropics, who has 

 generally learnt its danger by personal experience. 



Radiation takes place best when the air is still, dry, and cold, conduction 

 when it is damp. Convection is only of importance when the air is in motion, 

 in which case the loss of heat is proportionate to the square root of the velocity, 

 and is more marked when atmospheric humidity is high. 



With regard to evaporation, Rubner has shown that it is best at medium, 

 greater at low, and still greater at high temperatures, as is shown by the 

 following table taken from his book of an observation on a man of 58 kilo- 

 grammes weight lightly clad: — • 



1. Temperature and conductivity of the skin. 



2. Temperature and radiation from the skin. 



3. Temperature of the air. 



4. Rate of motion of the air. 



Air Temperahtre. 



Grammes of OH^ 

 per Hour. 



Grammes of CO^ lost 

 per Hour. 



2° C. 



37 

 28 



19 

 23 

 43 

 84 



29-8 

 25-1 



24- 1 



25- 0 

 25*3 

 23-7 



10° to 15° C. 

 15° to 20° C. 

 20° to 25° C. 

 25° to 30° C. 

 30° to 35° C. 

 35° to 40« C. 



112 



21'2 



