84 PHYSIOLOGY 



warm; if they are contracted, one feels cold. For this 

 reason if there is little blood in the skin, one may feel 

 cold even when the body is burning with fever. 



Effect of Alcohol on Body Temperature. — Alcohol 

 prevents the surface blood vessels from responding 

 readily to changes in temperature. A drunken man 

 exposed to great cold is apt to freeze to death, for the 

 relaxed surface blood vessels contain so large a quantity 

 of blood that heat is given off much faster than it is 

 produced. At the same time he may have a pleasure- 

 able sensation of warmth because of the unusual amount 

 of blood in the skin. 



Adaptation of the Circulation to Bodily Need. — Pos- 

 sibly no other system has so many adaptations by which 

 accidental defects correct themselves as the circulatory 

 system. The clotting of the blood and the contraction of 

 the vessels, which, following directly upon an injury, 

 prevent bleeding to death, and the action of the surface 

 blood vessels, which, through heat, are stimulated to 

 cause the body to give off heat, and, through cold, are 

 stimulated to cause the body to conserve its heat, have 

 already been mentioned. In addition, we find that if 

 the heart is stretched by an increased quantity of blood 

 so that a harder beat than usual is necessary to force it 

 out, the stretched muscle is able to beat harder than the 

 unstretched muscle; if continued hard work is de- 

 manded, the work itself strengthens the muscle. It 

 grows thicker in response to the demand made upon it 

 and it gains strength to meet the demand. If, however, 

 too great a demand is made, as in the case of some 

 athletes, the heart muscle becomes so thick that it can 



