THE TEMPERATURE OF THE BODY 499 



through a much greater depth of atmosphere; hence the greater 

 splendour of the colours. 



As the temperature of the air and surrounding objects is made to 

 approach that of the body, loss by radiation and convection becomes 

 small, then nil. Finally, as the air temperature comes to exceed 

 that of the body, heat passes from the air to the body. The body, 

 however, does not become heated so long as the air is dry. The 

 sweat glands come into action, and the body heat continues to be lost 

 by conversion of water into aqueous vapour. The difficulty of main- 

 taining the thermostatic equilibrium of the body increases when the 

 conditions become such that the whole elimination of heat is by 

 evaporation. 



A man can stay in a dry atmosphere at a temperature sufficient 

 to cook his dinner. He can keep cool by sweating. He cannot 

 stand a water or steam bath above body temperature without becom- 

 ing overheated. Immersion for a few minutes in a bath at 110 F. 

 raises the rectal temperature to 103 F., greatly accelerates the breath- 

 ing and pulse, lowers the arterial pressure, and flushes the skin. On 

 standing up suddenly, a sense of faintness ensues. A cold shower- 

 bath taken now at once constricts the skin, slows the pulse, raises the 

 blood -pressure, and removes all sense of faintness, while the rectal 

 temperature still remains at 103 F. 



Baths cold and hot are a most potent means of altering the meta- 

 bolism both of the skin and of the whole body. 



The amount of heat lost by evaporation is very great under con- 

 ditions of hot dry atmosphere. Thus, it was estimated that 10 litres 

 of water were lost from the body during a ride at a temperature of 

 45 C. in South California. 



In a dry hot atmosphere, such as the stokehole of a steamer in 

 the tropics, the men are kept cool by sweating, the forced draught of 

 air to the furnace insuring this. The amount of drink required may be 

 enormous e.g., 15 pints of water a day. In certain factories, mines, etc., 

 where the air is warm and moist, it is of great economic importance 

 to keep the air in movement, or the vapour pressure down to a level 

 commensurate with the performance of efficient work, and main- 

 tenance of comfort and health. A regulation made for weaving- 

 sheds and spinning-mills is that the wet-bulb thermometer should not 

 be allowed to rise above 75 F. 



The amount of water lost from the body during a march may be 

 calculated by weighing the body before and after the march, supposing 

 no food or drink is taken, and no faeces or urine passed during the 

 march. The weight of oxygen taken in balances approximately the 

 weight of carbonic acid given out. The water retained in the clothes 

 may be estimated by weighing the clothes before and after the march . 

 Such estimations, coupled with those of pulse-rate and body tempera- 

 ture, have shown the value to soldiers of opening or taking off their 

 tunics in hot weather. If the evaporation of sweat and convection 

 is made easy, fatigue and danger of heat-stroke are prevented. It 

 has been calculated that a resting soldier weighing 70 kilogrammes, 



