238 SCIENCE OF COMMON (THINGS. 



Why a dead body is cold. "Why we perspire. 



The lungs throw off almost all of it into the air, by 

 the act of respiration. 



1595 Does the heat of the human body arise from the same cause as 

 the heat of fire ? 



Yes, precisely. The carbon of the blood combines 

 with the oxygen of the air inhaled, and produces car- 

 bonic acid gas, which action developes heat. 



; 1590 If animal heat is produced by combustion, why does not the 

 human body burn up like a coal or candle ? 



It actually does so. Every muscle, nerve, and organ 

 of the body actually wastes away like a burning candle 

 and (being reduced to air and ashes) is rejected from 

 the system as useless. 



1597 If every bone, muscle, nerve, and organ is thus consumed by com- 

 bustion, why is not the body entirely consumed? 



It would be so, unless the parts destroyed were per- 

 petually renewed ; but as a lamp will not go out so long 

 as it is supplied with fresh oil, neither will the body be 

 consumed so long as it is supplied with sufficient food. 



1598 What is the principal difference between the combustion of a fire 

 or lamp, and that of the human body ? 



In the human body, the combustion is effected at a 

 much lower temperature, and is carried on more slowly, 

 than it is in a lamp or fire. 



1599 Why is a dead body cold? 



Because air is no longer conveyed to the lungs after 

 respiration has ceased ; and therefore animal heat is 

 no longer generated by combustion. 



1600 Why do we perspire when very hot ? 



The pores of the body are like the safety-valves of a 

 steam-engine ; when the heat of the body is very great, 

 some of the combustible matter of the blood is thrown 

 off in perspiration, and the heat of the body is thereby 

 reduced. 



1601 Why does exercise make us warm ? 



Because we inhale air more rapidly when we exer- 

 cise, and cause the blood to pass more rapidly through 

 the lungs in contact with it. 



