METABOLISM 



233 



water from the skin; evaporation of water from the nasal passages and 

 the lungs; expiration of the warmed air; excretion of the warm urine and 

 of the warm feces. Of these, radiation and conduction account for 

 about 73 per cent, of the heat lost. In other words, about three-quarters 

 of the heat made in the body is lost by warming its surroundings, air, 

 water, bedclothes, clothing, chairs, etc. Evaporation from the skin 

 loses probably about 15 per cent, of the total quantity of heat. Evapora- 

 tion from the nasal passages and lungs expends not far from 7 per cent, 

 of the total heat lost, while about 3 per cent, goes off in the expired air. 



FIG. 127 



AREA CONTENTS RATIO 



J_ 



AREA CONTENTS RATIO 



AREA, 96 3 



CONTENTS, 64 2 



AREA, 24 3 



CONTENTS, 8, T 



This diagram shows that in two animals of like shape the smaller may have twice as much 

 surface-area (heat-loss) in proportion to its contents (heat-production) as the larger. 



The term Thermotaxis, the regulation of body-heat, meaning 

 literally "heat-arrangement," has already been met with in the chapter 

 on Protoplasm (see page 43), and there indicates the reaction to heat 

 of the entire body at once in case of certain small and simple 

 organisms. As applied to man, etc., its meaning is somewhat different 

 in that it indicates adjustment of parts of the organism to special thermic 

 conditions. The arrangements in the human body by which these 

 adjustments are brought about constitute one of the most elaborate 

 mechanisms of the organism. By its means the temperature is kept 

 constant despite the obvious wide variations in climate, food, dress, 

 labor, etc. 



