CIRCULATION 1 2 I 



part to be a specific manifestation of the unexplained but rather general 

 loss of elasticity of many tissues in old age. This effect upon the skin of the 

 aged is known to all. But many aspects of hardening of the arteries are 

 puzzling. The narrowed caliber of the vessels and the change in structure 

 of the walls have not as yet been satisfactorily accounted for. 



Usually associated with hardening of the arteries is a chronic eleva- 

 tion of the arterial blood pressure. The systolic pressure may rise to 250 

 or 300 mm. Hg. By some, this is looked upon as a compensatory adjust- 

 ment, by which blood is forced through the narrowed vessels, and a more 

 or less adequate circulation is maintained. The seriousness of high blood 

 pressure (hypertension) lies partly in the danger that some blood vessel 

 may rupture. Rarely does this occur in large vessels, with dangerous ex- 

 tensive hemorrhage. More often it involves vessels of such size that the 

 loss of blood per se is not important. But if this bleeding occurs in a vital, 

 and particularly a friable, structure like the brain, serious damage may 

 result. Many brain cells may be torn and damaged by the blood escaping 

 under high pressure. Everyone knows of individuals who have suffered 

 such a "cerebral accident," which often causes paralysis, and is commonly 

 known as a "stroke." The rationale of having people with high blood pres- 

 sure lead as quiet a life as possible is obvious when we recall that muscular 

 exercise and excitement elevate the arterial blood pressure. This, of course, 

 would increase the danger of rupturing a vessel. 



LYMPH AND LYMPH VESSELS 



The lymphatic system is a circulatory system having rather intimate 

 anatomical and physiological interrelationships with the blood-circulatory 

 system, similar to it in certain respects and quite different in others. Lymph 

 vessels, like blood vessels, are distributed to all parts of the body. We may 

 liken the system anatomically to the capillaries-plus-veins portion of the 

 blood-circulatory system. The lymphatic system possesses no counterpart 

 of the arteries and, consequently, does not have a true continuous closed 

 circulation. The fluid of the vessels, called "lymph," enters the system in 

 the lymph capillaries, which resemble other capillaries except that they 

 appear to be closed at their terminal ends. The lymph flows from the capil- 

 laries of all parts of the body into larger and larger vessels resembling 

 veins in that they possess valves and are thin walled. In fact, the lymph 

 vessels have even thinner walls than the veins. Larger and larger vessels 

 finally converge to the left-shoulder region in the thorax, where the lymph 

 empties into a large vein of the blood-circulatory system. 



But where does the lymph come from? From where does it pass into 

 the closed lymph system? Lymph, in general, originates as tissue fluid — 

 the fluid which surrounds all cells. This, in turn, has reached the cells 

 from the capillaries of the blood-circulatory system. Thus fluid may 

 reach the cells by only one route — the arteries, arterioles, and finally capil- 



