CIRCULATION OF THE BLOOD. 109 



236. Although the heart sends the blood by the same 

 impulse to all the arteries, and all these must then beat, al- 

 most at the same moment, and in unison, yet the expansion 

 and contraction of these blood-vessels are not always the 

 same in all parts of the body. Hence the blood may circu- 

 late with very different force in various parts, and some may 

 be supplied very freely while others are but sparingly fed 

 with this fluid. Local diseases create a greater local circu- 

 lation. When one has a felon on his finger, he feels the 

 arteries throb sometimes violently in the sides of that fin- 

 ger, while the beating of the arteries in the other fingers is 

 scarcely noticed. Some suffer from cold feet in consequence 

 of feeble circulation of blood through those extremities ; 

 others have headaches from the too great flow of blood to the 

 brain. The arteries are more active in the parts that are in 

 action. More blood flows to the muscles during the time of 

 labor, to the stomach during digestion, and to the brain when 

 the mind is actively employed. 



237. This beating of the heart, and this pulsation of the 

 arteries, are incessant during life. Day and night, asleep or 

 awake, this movement goes on, and every part of the frame 

 receives its supply of blood in due season, without our voli- 

 tion, and even without our observation. The circulation of 

 the blood is not submitted to our care, and we are not respon- 

 sible for its work, as we are for the work of digestion. Yet, 

 though we are not called upon to aid this function, we may 

 interfere for evil. We may, by stimulating food or drinks, 

 excite the heart too much for health; or, by neglect of 

 proper exercise, we may suffer it to become sluggish in its 

 motions. 



10 



