206 OUR BODIES AND HOW WE LIVE 



The lungs have also been described in a previous chapter. 

 One duty of the lungs, as we have learned, is to excrete carbon 

 dioxide, watery vapor, and a small quantity of other wastes. 



278. The Kidneys. The kidneys, two important organs 

 of excretion, are of a brownish-red color, about four inches 

 long and two inches wide, and of the shape of a kidney 

 bean. They lie in the region of the loins, in front of the 

 backbone, behind the intestines, one on each side, and are 

 imbedded in fat. A sheep's kidney is a familiar sight in a 

 market. It is very much like the same organ in man. 



279. The Structure of the Kidneys. The kidneys are 

 made up of bundles of long tubes, not so very unlike sweat 

 glands. These tubes are surrounded by a meshwork of 

 capillaries. They are very fine, threadlike structures, not 

 more than a five-hundredth of an inch in diameter. Thus, 

 there are thousands upon thousands of them packed together 

 in each kidney. 



The blood filters certain waste matters dissolved in 

 water into these tubes, just as it gives up sweat to the 

 sweat glands. These tubes unite into one common duct 

 from each kidney, which carries away the excretion. In 

 due time this waste material is cast out of the body. 



The kidneys thus serve as a peculiar and delicate kind 

 of filter, carrying off urea, inorganic salts, and other waste 

 matters dissolved in a large quantity of water. 1 



280. The Work done by the Kidneys. About three pints 

 of fluid are daily discharged, on an average, through the 



1 The whole of this excretion is called the urine. It is in reality water, 

 holding in solution urea and several salts. The urine is constantly being 

 secreted by the kidneys. It is carried to the bladder, which serves as a 

 reservoir. It collects in the bladder until this receptacle is nearly full, 

 when it is emptied by the contraction of its walls, aided by the abdominal 

 muscles. 



