364 A YEAR IX SCIEXCK 



heat is given up to the cooler parts. Heat also travels 

 by conduction from the warmer to the colder parts. 



Cooling' the body. Usually too much heat is pro- 

 duced. The body is then brought to the proper tem- 

 perature by cooling, a process which is brought about 

 through the skin. If the body is too warm, the blood 

 vessels in the skin enlarge and the blood supply to the 

 skin is greatly increased. As a result the skin becomes 

 very warm. It is then cooled by radiation, conduction, 

 and by the evaporation of perspiration. 



We can easily feel the heat given off by the skin 

 through radiation and conduction. If too much heat 

 is being lost in this way, the blood vessels in the skin 

 contract and less blood flows through it. Perspiration 

 is being produced nearly all the time. If the body is 

 not warm, the amount of perspiration is small and 

 dries up as soon as it is produced. , If, however, the 

 body becomes very warm because of increased activity 

 in work or play, or if the surrounding temperature is 

 very high, more perspiration is produced. The body 

 becomes covered with a layer of water. In order to 

 evaporate this, heat is taken from the skin ; in this way, 

 the temperature is lowered. 



By radiation and conduction it would be impossible 



to cool the body if the temperature of the atmosphere 







was over 98.5 F. By the evaporation of perspiration, 

 however, the temperature can be lowered even in the 

 torrid regions. 



All of this fine adjustment between the amount of 



