68 APPLIED PHYSIOLOGY 



126. Regulation of the flow of blood. When a cell is 

 working hard, it needs more food than when it is still. 

 Nature provides more food for a working part in two ways : 



First. The muscles in the arteries relax, so that the 

 tubes become larger. Then more blood flows through the 

 part. When you run, your face looks red from this cause. 



Second. The heart itself beats faster and with greater 

 strength. After a race you can feel your heart beat 

 within your chest In these two ways nature always pro- 

 vides the exact amount of food which each part needs. 



127. Effects of too much exercise. During severe work 

 the heart works harder, so as to provide food for the 

 cells. This soon wears out the heart, so that it cannot 

 send enough blood even for light work. Boys can run or 

 work as hard as they please for a minute or two at a time 

 and will not be harmed. But they often try to see which 

 one can run the farthest or lift the most. Then they may 

 get very tired and may so weaken their hearts that they 

 never recover. 



128. Fainting. When the heart beats with little force, 

 or stops beating, the cells suffer at once. The brain suf- 

 fers sooner than any other part. Then the mind stops 

 acting, and the person is faint. His face is white, for it 

 has no blood, and he is in a deep sleep. 



When a person faints, lay him down with his head low, 

 so that blood will go to the brain. Rub his arms and legs 

 towards his body to drive the blood to his heart. Also 

 throw cold water on his face to cause the heart to beat 

 harder. In a moment or two he will revive and be as well 

 as before. 



129. Alcohol and blood. Alcohol hinders the digestion 

 of food and weakens the liver so that it cannot change 

 the food to blood as it should. Thus the blood carries too 



