KIDNEY BEAN, a bean of the genus Phaseolus, of which European species and varieties have been cultivated from a time im memorial. (See BEAN). The wild kidney bean of the United States is a high-climbing vine (P. polystachyus), bearing small purple flow ers. The so-called "kidney-bean tree; is Wis taria (q.v.).
the purple boneset (q.v.). KIDNEYS, the principal excreting organs of the body. They are two in number, fixed at the back of the abdominal cavity by a thick layer of fat and the peritoneum which passes in front of them; their lower border is slightly below the last ribs; they have an outer, upper and lower convex margin and an inner margin deeply indented, allowing the entrance of the renal artery and exit for the veins and ureter. This indentation corresponds to a considerable hollowing of the interior, which is occupied by the funnel-like origin of the ureter (the pel vis). The kidney is surrounded by a firm mem brane called the capsule; inside of this is the substance proper, made up of a connective-tissue groundwork, in which are embedded the blood vessels sand the secreting glands called the uri niferous tubules. These tubules start in tiny rounded bodies (Malpighian bodies), and after an orderly arrangement of windings a number of the tubules form slightly larger tubules (col lecting tubules), so grouped together as to form striated pyramids which have their apices pro jecting into the pelvis of the kidney. By a process similar to filtration the excess of water in the blood passes through these walls and out of the body. There is a similar arrangement of the blood-vessels around the winding tu bules, but through these the solids in solution in the blood that are of no further use to the body are taken up by the epithelium of the tubules them occur in too great a proportion. This implies an extraordinary adaptability of the functions of the kidneys to the requirements of the animal organism. It registers and re acts to the formation by metabolism of sub stances soluble and non-volatile in every tis sue of the body wherever located. When urea.
and added to the watery element inside the tubes. The purpose of the kidneys is the ex
cretion of constituents, all of which are formed before they are delivered to the kidney by other organs, kith the exception of hippuric acid, which alone is secreted by the kidneys them selves. Their duty, therefore, is to rid the blood of abnormal constituents or indeed any of its normal constituents if they or any bf uric acid or water is taken up from the sur rounding lymph, it is discharged into the cavi ties of the kidneys, from which it is drawn off by the ureter into the bladder, where it is stored until a time suitable for its ejection. Not only is this the case, but if for any reason too much of any given ingredient has been taken out of the blood it is returned. As an exact measurement it is interesting to note that about 1,700 litres of blood flow through the two kid neys in a living human each 24 hours, and from the blood 30 litres of waste matters are finally taken out and ejected. The ureters are about 16 inches long, with the diameter of a goose quill ; they are lined by a mucous membrane, outside of which there are thin muscular and fibrous layers of tissue.
Urine.—The urine is an amber or yellOwL ish fluid containing about 95 per cent of water, having a specific gravity of 1.018 to 1.025, an acid reaction and rather characteristic ammo niacal odor. The inorganic solids held in solu tion are the chlorides, phosphates and sulphates of sodium, magnesium, potassium, calcium and iron. More important than these is a group of substances elaborated in the body during meta holism (q.v.), some of which may act as poi sons if not properly discharged; the principal ones being urea, uric acid, creatinine, hippuric acid and the xanthin bases. That of most im portance is urea, which should in normal adults be excreted to the amount of 500 grains daily. In certain forms of kidney disease the deficiency of this substance is taken as an in dex of the organ's impairment in respect to this one function. Other disturbances of function are tested by other tests. Thus chloride reten tion or water retention are other types of dis ordered function.