SUMMARY. 
229 
and the colder and heavier air rushes into its place. Thus a ivind is 
caused. 
Land and Sea Breezes.— These winds are due to the fact that land takes in 
heat, and also gives it out, more quickly than the sea does. Therefore, by day the 
land becomes hotter, and at night colder, than the sea. 
VENTILATION (p. 171). 
Reasons for Ventilation. — The air of a room is made impure 
by the waste matters passing off by the breath and the skin of persons in it. 
The changes in the composition of the air due to breathing (respiration) may be 
thus shown. In 10,000 parts of air there are : 
As it enters As it leaves 
the lungs. the lungs. 
Nitrogen, 7900 7900 
Oxygen, 2096 1630 
Carbonic acid gas, 4 470 
10,000 10,000 
HOW to Ventilate. — We must have an outlet for the foul air and 
an inlet for the fresh air, so as to keep the air moving. Draughts should be 
avoided; also the entry of malarial air. 
Ventilation may be provided by means of : 
1. Doorways, windows, or other openings. 
2. Special apparatus; such as tubes, gratings, &c. 
3. A space under the ground floor, where the air may circulate, so that 
harmful gases from the soil do not rise into the house. 
THE CLOTHES WE WEAR (p. 174). 
Uses of Clothing: 
1. To help to maintain an even temperature in every part of the body. 
2. To shield the body from the scorching rays of the sun. 
3. To absorb the perspiration. 
4. To keep the body from being wetted by rain or dew. 
5. To protect the skin from being torn or injured. 
Clothing should be: 
1. A bad conductor of heat; that is, it should not readily lead (or con- 
duct) the heat of the body away. 
2. Porous ; to allow impurities from the skin to 'pass through it. 
3. Absorbent ; to suck up the perspiration and pass it outwards to the 
air. 
4. Not heavy. 
