The liability of the lungs to attacks from such dread diseases as consumption and pneumonia makes questions touching their hygiene of first importance. Consumption does not as a rule attack sound lung tissue, but usually has its beginning in some weak or enfeebled spot in the lungs which has lost its "power of resistance." Though consumption is not inherited, as some suppose, lung weaknesses may be transmitted from parents to children. This, together with the fact, now generally recognized, that consumption is contagious, accounts for the frequent appearance of this disease in the same family. Consumption as well as other respiratory affections can in the majority of cases be _prevented_, and in many cases cured, by an intelligent observation of well-known laws of health. *Breathe through the Nostrils.*—Pure air and plenty of it is the main condition in the hygiene of the lungs. One necessary provision for obtaining _pure air_ is that of breathing through the nostrils. Air is the carrier of dust particles and not infrequently of disease germs.(33) Partly through the small hairs in the nose, but mainly through the moist membrane that lines the passages, the nostrils serve as filters for removing the minute solid particles (Fig. 45). While it is important that nose breathing be observed at all times, it is especially important when one is surrounded by a dusty or smoky atmosphere. Otherwise the small particles that are breathed in through the mouth may find a lodging place in the lungs. [Fig. 45] Fig. 45—*Human air filter.* Diagram of a section through the nostrils; shows projecting bones covered with moist membrane against which the air is made to strike by the narrow passages. 1. Air passages. 2. Cavities in the bones. 3. Front lower portion of the cranial cavity. In addition to removing dust particles and germs, other purposes are served by breathing through the nostrils. The warmth and moisture which the air receives in this way, prepare it for entering the lungs. Mouth breathing, on the other hand, looks bad and during sleep causes snoring. The habit of nose breathing should be established early in life.(34) *Cultivate Full Breathing.*—Many people, while apparently taking in sufficient air to supply their need for oxygen, do not breathe deeply enough to "freely ventilate the lungs." "Shallow breathing," as this is called, is objectionable because it fails to keep up a healthy condition of the entire lung surface. Portions of the lungs to which air does not easily penetrate fail to get the fresh air and exercise which they need. As a consequence, they become weak and, by losing their "power of resistance," become points of attack in diseases of the lungs.(35) The breathing of each individual should receive attention, and where from some cause it is not sufficiently full and deep, the means should be found for remedying the defect.