388 RESPIRATION AND EXCRETION 



Many of the bacteria present in the air are active in causing 

 diseases of the respiratory tract, such as diphtheria, membranous 

 croup, and tuberculosis. Other diseases, as colds, bronchitis 

 (inflammation of the bronchial tubes), and pneumonia (inflam- 

 mation of the tiny air sacs of the lungs), are probably caused by 

 bacteria. 



Dust, with its load of bacteria, will settle on any horizontal sur- 

 face in a room not used for three or four hours. Dusting and 

 sweeping should always be done with a damp cloth or broom, 

 otherwise the bacteria are simply stirred up and sent into the air 

 again. The proper watering of streets before they are swept is 

 also an important factor in health. 



Ventilation of Sleeping Rooms. Sleeping in close rooms is 

 the cause of much illness. Beds ought to be placed so that a 

 constant supply of fresh air is given without a direct draft. This 

 may often be managed with the use of screens. Bedroom windows 

 should be thrown open in the morning to allow free entrance of the 

 sun and air, bedclothes should be washed frequently, and sheets 

 and pillow covers often changed. Bedroom furniture should be 

 simple, and but little drapery allowed in the room. 



Hygienic Habits of Breathing. Every one ought to accustom 

 himself upon going into the open air to inspire slowly and deeply 

 to the full capacity of the lungs. A slow expiration should follow. 

 Take care to force the air out. Breathe through the nose, thus 

 warming the air you inspire before it enters the lungs and chills 

 the blood. Repeat this exercise several times every day. You will 

 thus prevent certain of the air sacs which are not often used from 

 becoming hardened and permanently closed. 



The Relation of Tight Clothing to Correct Breathing. It is im- 

 possible to breathe correctly unless the clothing is worn loosely 

 over the chest and abdomen. Tight corsets and tight belts prevent 

 the walls of the chest and the abdomen from pushing outward and 

 interfere with the drawing of air into the lungs. They may also 

 result in permanent distortion of parts of the skeleton directly under 

 the pressure. Other organs of the body cavity, as the stomach and 

 intestines, may be forced downward, out of place, and in conse- 

 quence do not perform their work properly. 



Relation of Exercise. We have already seen that exercise re- 



