main channels, the lungs, skin, and kidneys, and the materials are of four kinds, urea, carbon dioxide, salts, and water. The lungs carry off carbon dioxide and water chiefly, the skin these and inorganic salts, while the kidneys eliminate practically all the urea as well as inorganic salts and water. When the kidneys are not working the skin carries off much urea. In fact, a close relationship exists between the kidneys and the skin in the matter of excretion. Thus, with increased perspiration in warm weather comes decreased urine, while in cold weather the blood is sent in and the urine increased in amount.
To incite action of the kidneys drugs known as diuretics may be used. These act in two ways, by stimulating the kidney cells directly and by acting on the general circulation or nervous system. Any emotional or nervous excitement increases the flow of urine.
There are certain abnormal constituents of urine, of which the two most important are albumen and sugar. The former is found only when there is some disturbance of the kidneys, ureters, or bladder, and its presence usually denotes some change in the cells lining the urinary tract. It may occur in congestion of the kidney as well as in disease. Sugar is found only in diabetes, the amount varying with the severity of the disease. In jaundice certain bile pigments are present in the urine, giving it a dark brown color and to the foam a greenish-yellow color. Even normal urine has some sediment upon standing, consisting of cells from the urinary tract and mucus. In very acid urine after standing a heavy sediment, whitish or pinkish, i.e., brick dust, in color, is thrown down. It does not necessarily denote disease, but shows the urine is acid and concentrated. In alkaline urine there is a sediment due to phosphates.
Rupture of the kidney occurs but is not so serious as rupture of the liver or spleen because the kidney is sit-
