HEAT AND CLOTHING 235 



The production of heat also depends upon the amount 

 of oxygen taken into the body. In work, deeper inspira- 

 tions are taken, and more oxygen reaches the cells, and 

 thus exercise warms the body. 



411 . Regulation of the heat given off. Nature also 

 regulates the amount of heat given off. The body loses 

 some heat through the breath, and more by contact with 

 the cool air. When the temperature of the inside of the 

 body is raised, the blood tubes of the skin dilate, so that 

 more blood comes in contact with the air. If the tempera- 

 ture falls slightly below the natural point, the blood tubes 

 of the skin contract, so that less blood comes to the sur- 

 face, and more heat is retained until the temperature rises 

 to the natural point again. A change of temperature too 

 small to be felt will produce these changes in the blood 

 tubes of the skin. 



412. Effects of tight bands. When the circulation is hindered 

 so that less blood enters any part of the body, its temperature falls. A 

 finger whose veins are compressed by a tight string becomes percepti- 

 bly cooler in less than a minute. Garters often cause cold feet in the 

 same way. Compression of the waist may cause the whole body to feel 

 cold. 



413. Effects of perspiration. Sometimes men work in 

 air which is hotter than their bodies. Then instead of 

 giving, they receive heat. In order to keep them cool 

 under these circumstances, nature has provided a self- 

 acting bath by means of the sweat, ox perspiration. When 

 the temperature of the body is raised from any cause, the 

 perspiration is poured out in greater quantity, which in- 

 creases as the quantity of heat increases. 



The heat of the body is used in changing the water of the perspira- 

 tion to steam, which then passes off from the body. The process is 



