16 THE HUMAN BOD?. 



differently arranged to receive the air which we breathe-in,. 

 and expel after abstracting from it part of its oxygen and 

 adding to it certain other things; and in the heart and 

 blood-vessels we find almost the same tissues arranged to 

 propel and carry the blood over the whole Bodv. The 

 working of the Body offers clearly even a more complex 

 subject of study than its structure. 



Physiological Properties,, In common with inanimate 

 objects the Body possesses many merely physical properties, 

 as weight, rigidity, elasticity, color, and so on; but in ad- 

 dition to these we find in it while alive many others 

 which it ceases to manifest at death. Of these perhaps 

 the power of executing spontaneous movements and of 

 maintaining a high bodily temperature are the most 

 marked. As long as the Body is alive it is warm and,. 

 since the surrounding air is nearly always cooler, must be 

 losing heat all day long to neighboring objects; neverthe- 

 less we are at the end of the day as warm as at the begin- 

 ning, the temperature of the Body in health not varying 

 much from 37.5 C. (99 F.), so that clearly our Bodies 

 must be making heat somehow all the time. After death this 

 production of heat ceases and the Body cools down to the 

 temperature in its neighborhood; but so closely do we 

 associate with it the idea of warmth that the sensation 

 experienced on touching a corpse produces so powerful 

 an impression as commonly to be described as icy cold. 

 The other great characteristic of the living Body is its 

 power of executing movements; so long as life lasts it is 

 never at rest; even in the deepest slumber the regular 

 breathing, the tap of the heart against the chest-wall, and 

 the beat of the pulse tell us that we are watching sleep and 

 not death. If to this we add the possession of conscious- 

 ness by the living Body, whether aroused or not by forces 

 immediately acting upon sense-organs, we might describe 

 it as a heat-producing, moving, conscious organism. 



The production of heat in the Body needs fuel of 

 some kind as much as its production in a fire; and every 

 time we move ourselves or external objects some of the 

 Body is used up to supply the necessary working power, just- 



