112 ELEMENTS OF PHYSIOLOGY 



breaking out of perspiration. Why is this ? Certainly the 

 water does not reach the skin so quickly. The cold in 

 the interior stimulates the internal vessels to contraction 

 and the blood is diverted to the unstimulated vessels of the 

 skin, surrounding the sweat glands. 



193. Effects of Unusual Exercise. If a person has 

 sedentary habits and has neglected active exercise for 

 some time, the heart, as well as the other muscles, becomes 

 weak. If such a person hurries to catch a train, or takes 

 very rapid and trying exercise of any kind, he may bring 

 on an unpleasant palpitation of the heart, which is a warn- 

 ing to desist at once. Violent exercise should not be taken 

 until one has gradually led up to it. 



194. Sleep and the Blood. A person who loses much 

 sleep becomes pale ; the paleness is evidence of a diminu- 

 tion in the number of red corpuscles. It is during sleep 

 that the corpuscles that have been worn out during the day 

 are replaced, but loss of sleep causes a greater loss to the 

 blood than usual, with less than the usual opportunity for 

 repair. 



195. Mental Influences. Rage excites and strains the 

 heart. The unexpected receipt of joyful news sometimes 

 so acts upon the heart through the emotions as to cause 

 death. Thinking intently of an organ may cause an in- 

 crease of the circulation in it. 



196. Clothing. The blood cannot circulate with perfect 

 freedom unless the entire body is so loosely clothed that 

 there is no pressure upon any of the blood vessels, no 

 interference with the lungs as they expand, no pressure 

 upon the stomach, liver, and intestines. Many of the 

 largest veins, particularly those of the arms and legs, lie 

 so near the surface that any tightness of the clothing 

 is certain to diminish the flow of blood through them. 

 Sleeve supporters and garters, if used at all, should be 

 of weak elastic with adjustable buckle, and no tighter 



