Page:The New International Encyclopædia 1st ed. v. 02.djvu/105

ARTERY. The diseased conditions affecting arteries consist of (1) degeneration of the arterial walls (of either fatty, calcareous, or hyaline variety); (2) arterio-sclerosis: and (3) aneurism. Fatty degeneration of the intima (or inner coat of an artery) is very common. It occurs as yellowish spots in the aorta and larger vessels. Calcareous defeneration succeeds the fatty change, and occurs as Hakes or plates of chalky deposit in the intima. It is the terminal stage of arteriosclerosis. Hyaline degeneration is a change usually found at the beginning of arterio-sclerosls. It occurs as a smooth, homogeneous substance replacing the tunica intima, generally distributed throughout the smaller arteries and capillaries, especially in the kidney. The substance which replaces the normal tissue of the arterial coat is called atheroma (from Greek athērē, meal), whether hyaline, fatty, or calcareous; it consists of a pulpy or hardened mass of cholestrine, oil, albuminous and chalky material. In some arteries, such as those over the temples and at the wrists, chalky deposits or atheromatous thickening may be felt easily. Atheromatous deposit is at first attended with a narrowing of the calibre of the vessel, varying with the thickness of the deposit, and most marked at the points of bifurcation. Smaller arteries may be completely obliterated, while the larger arteries may be very much contracted. A later consequence is dilatation of the vessel. The power of the outer coats being insufficient to compress the deposit and to close in upon the blood, with which each contraction of the left ventricle of the heart distends them, they remain wide and distended during the relaxation of the ventricle, and the artery thus slowly expands; the enlargement being most marked at parts where there is most obstruction to the blood-current — as, for example, in curved arteries. These dilatations are apt to terminate in regular aneurism. The arteries sometimes become abnormally lengthened, and consequently become not only dilated, but also tortuous. Another condition involving much danger is this: an ossified artery loses the smoothness which the interior of the vessel ought to present, and from the displacement or cracking of a bony plate, there may be sharp, rough projections exposed, to which the fibrin of the circulating blood may adhere. These little clots, becoming detached, may be carried with the blood till they become arrested, and plug up an artery, thus presenting cases of embolism or thrombosis (q.v.). A blow may crush a diseased artery, when a healthy elastic vessel might have escaped injury. A ligature applied to any ossified artery is very apt to cause it to break, and the difficulty of securing such vessels is often very great. It is to this form of disease that most of the failures of operations for aneurism are due. The heart's action in pumping blood throogh stiff, unyielding arteries whose calibre is diminished causes a permanent rise in the blood pressure, resulting in hypertrophy of the heart, disease of the kidneys, cerebral hemorrhage, aneurism, gangrene or sclerosis of the coronary arteries. The treatment of disease of the arteries consists in removing the cause when possible, maintaining a quiet, well-regulated life, and the adherence to hygienic rules. Arteritis, or inflammation of the arteries, is no longer recognized by physicians as a specific general disease. See ; ; ; ; ; and.

ARTESIAN (ar-te'zh«n) WELLS (from the old county of Artois, Lat. Artesia, now part of France, where the oldest well in Europe was bored in 1126). Vertical borings into the ground, to a depth of 100 feet or more for the purpose of obtaining water from some deeply buried porous stratum, such as sandstone or gravel. In the true artesian well the water should flow to the surface, but at present the term artesian is applied to any deep well, even where the water is obtained by pumping.

The presence of an artesian water supply in any region depends upon the existence beneath that region of a tilted porous layer, inclosed between two impervious beds. The outcropping edge of the porous bed must, moreover, be of sufficiently open texture to soak up the rain which falls upon it, and furthermore there must be no escape of the contained water from the lower portions of the bed. It is therefore evident that when such a porous stratum is saturated with water, the latter will be under pressure, the pressure at any one point amounting to that of a column of water whose height is the difference between the altitude of that point and the altitude of the outcrop of the water-bearing layer. If now from a point on the surface, at a level lower than that of the outcrop of the porous stratum, a drill hole be sunk to the water-bearing bed, a flow of water will be obtained, but the water will seldom rise to the same level as the point of intake owing to the friction which has to be overcome in flowing through the porous bed. The most favorable conditions are when the rocks form a basin, or when the inclined porous layer passes into an impervious one. The collecting area, or region drained by the porous stratum may be in the immediate vicinity of the well (a common case in shallow wells) or it may be at a distance of several hundred miles. In boring for artesian water a knowledge of the geological structure of the region is of highest importance. The work of the United States Geological Survey, aided by data contained from wells already bored, has demonstrated the existence of several extensive and well-marked artesian water-yielding areas. Thus a large part of Nebraska, South Dakota, eastern Colorado, and northwestern Kansas, obtains its artesian water from the Dakota sandstone, the collecting area of which is around the base of the Black Hills in South Dakota and along the eastern foothills of the Rocky Mountains. The Iowa wells derive their water from the Saint Peters sandstone, whose collecting area is in Wisconsin. Along the Atlantic coast, many wells obtain a supply of pure water from the southeasterly dipping Tertiary and Cretaceous beds underlying that area.

Artesian wells in all parts of the country yield a supply of water for domestic use, which in many instances is much purer than surface water. In the arid regions of the West they also serve the purpose of supplying water for irrigation, thus rendering fertile the soil of many districts heretofore non-productive.

The Chinese were acquainted with artesian wells, and in Europe they have been used for centuries — in France, England, Austria, and Germany; indeed, the basin-shaped structure of the Paris and London areas, with their alternating beds of clay and sand, has yielded the