388 HUMAN PHYSIOLOGY 



can be proved by exposing a sterilized gelatin plate to the air 

 in a schoolroom for a few moments.^ 



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 washed frequently, sheets and pillow 

 covers often changed. Bedroom furniture should be simple, and 

 but little drapery allowed. 



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 



* Ex}3ose two sterilized dishes containing culture media ; one in a room being 

 swept with a damp broom and the other in a room which is being swept in the usual 

 manner. Note the formation of colonies of bacteria in each dish. In which 

 dish does the most growth take place? 



