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TABLE OF CONTENTS.

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RESPIRATION AND VENTILATION.

Respiration-composition of inspired and expired air-quan-
tity of air breathed-amount of CO2 breathed out-
amount of fresh air required-variation in density of air
due to elevation and difference of temperature-Boyle's
law. Ventilation-natural ventilation-openings for
ventilation-artificial ventilation-heat-steam jets-
pumps-fans-ventilation by propulsion-report
heating and ventilation of schools. Practical work

on

26-43

PERSONAL HYGIENE EXERCISE-HABITS.

Personal Hygiene-exercise-rest-habits. Causes of disease
-constitution - heredity - idiosyncrasies — age sex.
Clothing materials-comparison of values-microscopic
appearance-clothing of children-injurious clothing—
poisonous dyes. School Hygiene. Practical work

114-139

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ADVANCED HYGIENE.

CHAPTER I.

AIR.

THE importance of a supply of pure air for all the rooms of a house is not yet realised by the public to the extent that it should be. In nearly all towns and villages there is a popular demand for a pure water supply, and yet the very people who will insist upon this are, in many cases, living year after year in rooms where the chimney is stopped up and the windows never opened. Children reared amidst such surroundings are liable to be rickety and tuberculous, and, even if they escape these diseases, their growth is stunted and their constitution permanently injured.

The relative importance of pure air to the body is easily understood when it is considered that there are cases on record of human beings living for five or six weeks without food, whereas deprivation of air causes death in four or five minutes.

Air is a mixture of gases in which each constituent preserves all its characteristic chemical and physical properties, the properties of air being a mean between the properties of its constituents. Its composition is not invariable. If air were a chemical compound its composition would be invariable, and its properties would bear no relation to the properties of its constituents.

AD. HYG,

1

The average volumetric composition of pure atmospheric be taken as

air may

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There are also variable quantities of water vapour, ammonia, organic matter, mineral salts, nitric acid, and traces of ozone; in towns sulphurous acid and sulphuretted hydrogen are present.

It is a remarkable fact that the composition of the air is practically the same in every part of the world. In midocean it differs but very slightly from the air in the open spaces of large towns. This extraordinary uniformity in composition is brought about by several forces which are always at work purifying the air. These are:

1. The rain, which, as it falls, washes the air free from most of the suspended impurities. It also removes the greater part of the organic impurities as well as any acid gases; e.g. oxides of sulphur, oxides of nitrogen, etc.

2. The winds, which dilute and sweep away impurities, and bring a supply of pure air to take their place. Diffusion also assists in the dilution of impurities.

3. The green parts of plants, which, when the sun is shining upon them, possess the power of absorbing carbon dioxide from the air, keeping the carbon as their food, and setting free the oxygen.

4. The oxygen in the air-especially when in the form of ozone-which gradually oxidises and renders harmless the organic matters.

Ozone may be detected in the open air of seaside and country places. It is oxygen in an extremely active condition, and is able to attack and render harmless any waste organic matter. When it does this it is converted

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