152 THE CIRCULATION 



17. Circulation. The blood is in constant motion during 

 life. From the heart, as a centre, a current is always setting 

 toward the different organs ; and from these organs a current 

 is constantly returning to the heart. In this way a ceaseless 

 circular movement is kept up, which is called the Circulation 

 of the Blood. This stream of the vital fluid is confined to 

 certain fixed channels the blood-vessels. Those branching 

 from the heart are the arteries ; those converging to it are the 

 veins. The true course of the blood was unknown before the 

 beginning of the seventeenth century. In 1619 it was dis- 

 covered by the illustrious William Harvey. Like many other 

 great discoverers, he suffered persecution and loss, but unlike 

 some of them, he was so fortunate as to conquer and survive 

 opjfosition. He lived long enough to see his discovery uni- 

 versally accepted, and himself honored as a benefactor of 

 mankind. 



nature of the blood they profess to purify, and of the means by which 

 their drugs could possibly purify it, make fortunes out of the credulity of 

 the public. I would warn you against this notion of ; purifying ' the 

 blood. The blood is not like a river into which anything can be intro- 

 duced from without. It gets rid of, or destroys, all substances which 

 intrude all which do not form part and parcel of its own structure ; or,, 

 failing in that, it ceases to act as living blood." George Henry Lewes. 



5. By Means of the Blood, Exercise Benefits the Whole Body. 

 "The employment of the muscles in exercise not only benefits their 

 especial structure, but it acts on the whole system. When the muscles 

 are put in action, the capillary blood-vessels with which they are supplied 

 become more rapidly charged with blood, and active changes tak place, 

 not only in the muscles, but in all the surrounding tissues. The heart is 

 thus required to supply more blood, and accordingly beats more rapidly 

 in order to supply the demand. A large quantity of blood is sent through 

 the lungs, and larger supplies of oxygen are taken in and carried to the 

 various tissues of the body." The oxygen engenders a large amount of 

 heat, which produces an action on the skin whereby the increase of heat 

 may be got rid of. By this means the skin is exercised, the perspiration 

 is poured forth, the surface is caused to glow and is kept in health. 

 "Not only are these organs benefited by the increased circulation of the 

 blood, produced by exercise, but wherever the blood is sent, changes of a 

 healthful character occur. The brain and the rest of the nervous system 

 are invigorated ; the stomach has its powers of digestion improved ; and 



17. Motion of the blood ? What is meant by the circulation of the blood? How con- 

 fined ? Discovery made by Harvey ? 



