Common Diseases of the Nose and Throat.--Catarrh is a disease to which people with sensitive mucous membrane of the nose and throat are subject. It is indicated by the constant secretion of mucus from these membranes. Frequent spraying of the nose and throat with some mild antiseptic solutions is found helpful. Chronic catarrh should be attended to by a physician. Often we find children breathing entirely through the mouth, the nose being seemingly stopped up. When this goes on for some time the nose and throat should be examined by a physician for _adenoids_, or growths of soft masses of tissue which fill up the nose cavity, thus causing a shortage of the air supply for the body. Many a child, backward at school, thin and irritable, has been changed to a healthy, normal, bright scholar by the removal of adenoids. Sometimes the tonsils at the back of the mouth cavity may become enlarged, thus shutting off the air supply and causing the same trouble as we see in a case of adenoids. The simple removal of the obstacle by a doctor soon cures this condition. (See page 395.) Organs of Excretion.--All the life processes which take place in a living thing result ultimately, in addition to giving off of carbon dioxide, in the formation of organic wastes within the body. The retention of these wastes which contain nitrogen, is harmful to animals. In man, the skin and kidneys remove this waste from the body, hence they are called the organs of excretion. [Illustration: Longitudinal section through a kidney.] The Human Kidney.--The human kidney is about four inches long, two and one half inches wide, and one inch in thickness. Its color is dark red. If the structure of the medulla and cortex (see figure above) is examined under the compound microscope, you will find these regions to be composed of a vast number of tiny branched and twisted tubules. The outer end of each of these tubules opens into the _pelvis_, the space within the kidney; the inner end, in the cortex, forms a tiny closed sac. In each sac, the outer wall of the tube has grown inward and carried with it a very tiny artery. This artery breaks up into a mass of capillaries. These capillaries, in turn, unite to form a small vein as they leave the little sac. Each of these sacs with its contained blood vessels is called a _glomerulus_. [Illustration: Diagram of kidney circulation, showing a glomerulus and tubule: _a_, artery bringing blood to part; _b_, capillary bringing blood to glomerulus; _b'_, vessel continuing with blood to vein; _c_, vein; _t_, tubule; _G_, glomerulus.] Wastes given off by the Blood in the Kidney.--In the glomerulus the blood loses by osmosis, through the very thin walls of the capillaries, first, a considerable amount of water (amounting to nearly three pints daily); second, a nitrogenous waste material known as urea; third, salts and other waste organic substances, uric acid among them.