34 



GENERAL SCIENCE 



the suffering is extreme remedies may be administered 

 solely to ease pain and conserve the strength of the patient. 

 In all muscular tissues the arteries, veins, and capillaries 

 blende in a perfect network of blood vessels. Through 

 them the blood must be kept moving in its round of circula- 

 tion so that the tissues may be properly nourished. The 

 blood is being continuously purified as it 

 passes through the lungs and kidneys and 

 other excretory organs. In the veins 

 there is especial need to urge the blood on 

 in order to lighten the -effort put forth by 

 the heart in forcing along a sluggish cir- 

 culation. The " blood pressure" which 

 the heart must maintain to keep the flow 

 of blood sufficiently rapid may overwork 

 and weaken it. There is a constant 

 menace of rupturing the walls of the 

 arteries or other blood vessels under any 

 abnormal pressure. 



In the veins the lining in places is so 

 arranged in folds as to form pockets. 

 These allow the venous blood to pass 

 on toward the heart freely enough, but 

 any backward flow is prevented as the 

 veins are compressed by muscular con- 

 tractions. Thus it is that muscular 

 activities result in a better circulation. 

 This brings more nourishment to the muscles themselves, 

 and maintains a better state of the whole body. 



In a rush of blood to an affected part of the body to 

 protect it from harm, and to repair any damage already done, 

 there is occasionally a congested state of the blood vessels 

 of that particular part. This is seen in the blood-shot 

 appearance of the eyeball, and the feverish condition of 



FIG. 13. Pocket- 

 like folds in the lining 

 of veins serve as 

 valves to prevent in 

 part any backward 

 flow of blood. 

 (Bundy.) 



