As a gas we take it in pure drinking water, and in larger proportions in soda water and other effervescing beverages ; also in the bread and cakes which are made light by its use. In these forms its effects on the stomach are wholesome. But its principal gaseous form is in the air we breathe, where it has been produced by our own respiration and that of all living animals, and also by the decay of all organic matter. We breathe in oxygen from the air and also carbon dioxide ; but when this carbon dioxide is diluted in the right proportion, as it is in the pure out-of-door air, its effects on our lungs are harmless. Because out of doors the plants, when in the sun- light, take in through their leaves the carbon dioxide which we have breathed out and they convert it into plant tissue. This helps to make the out-of-door air purer than that in- doors. The oxygen, which we breathe in, unites with the carbon in our blood, producing heat to keep us warm, and carbon dioxide which we must get rid of as quickly as pos- sible, by deep, full breathing. When there is an excess of it in the air, it is difficult for us to breathe. When there is more than a certain amount, we faint or suffocate. In the house this carbon dioxide which we breathe out remains in the rooms, and unless there is a constant supply of fresh air coming in, sufficient to blow this bad air away from us, we feel uncomfortable ; our lungs are hungry for more oxygen. When many persons are in a small, close room, or lamps and gas lights are giving out carbon dioxide, the air soon becomes dangerous to breathe. In some places air contains noxious gases, and everywhere there are floating particles of earthy matter, smoke and soot INTRODUCTION 3 which we can see ; also many very minute forms of Hfe, known as germs or microbes, which are invisible except under a powerful microscope. These floating particles are always in the air and you can see them by looking steadily at a ray of sunlight shining into the room. They are blown about here and there and are seldom motionless, but in the house where there is not suffi- cient air to keep them moving, they settle on floors and fur- niture where we can see them ; also on walls and many places where they are not visible : making what is usually called dust. Many of these dust germs, if they are in a warm moist place, can produce other tiny plants some of which are useful and help us in the changes which cooking produces in food. Yeast which we use in bread making is one variety of these useful plants. Mold on bread is an objectionable variety. Other germs are poisonous, and if we are weak, ill-fed, or have not sufficient oxygen in our blood to destroy these germs when they get into our system, they develop disease. Therefore to avoid them we must breathe plenty of pure air, keep ourselves and our food clean, and keep the air as clean as possible. Ventilation. We can improve the air in our rooms in several ways.

AI-modernized reading of the original text

As a gas we take it in pure drinking water, and in larger proportions in soda water and other effervescing beverages ; also in the bread and cakes which are made light by its use. In these forms its effects on the stomach are wholesome. But its principal gaseous form is in the air we breathe, where it has been produced by our own respiration and that of all living animals, and also by the decay of all organic matter. We breathe in oxygen from the air and also carbon dioxide ; but when this carbon dioxide is diluted in the right proportion, as it is in the pure out-of-door air, its effects on our lungs are harmless. Because out of doors the plants, when in the sunlight, take in through their leaves the carbon dioxide which we have breathed out and they convert it into plant tissue. This helps to make the out-of-door air purer than that indoors. The oxygen, which we breathe in, unites with the carbon in our blood, producing heat to keep us warm, and carbon dioxide which we must get rid of as quickly as possible, by deep, full breathing. When there is an excess of it in the air, it is difficult for us to breathe. When there is more than a certain amount, we faint or suffocate. In the house this carbon dioxide which we breathe out remains in the rooms, and unless there is a constant supply of fresh air coming in, sufficient to blow this bad air away from us, we feel uncomfortable ; our lungs are hungry for more oxygen. When many persons are in a small, close room, or lamps and gas lights are giving out carbon dioxide, the air soon becomes dangerous to breathe. In some places air contains noxious gases, and everywhere there are floating particles of earthy matter, smoke and soot INTRODUCTION 3 which we can see ; also many very minute forms of life, known as germs or microbes, which are invisible except under a powerful microscope. These floating particles are always in the air and you can see them by looking steadily at a ray of sunlight shining into the room. They are blown about here and there and are seldom motionless, but in the house where there is not sufficient air to keep them moving, they settle on floors and furniture where we can see them ; also on walls and many places where they are not visible : making what is usually called dust. Many of these dust germs, if they are in a warm moist place, can produce other tiny plants some of which are useful and help us in the changes which cooking produces in food. Yeast which we use in bread making is one variety of these useful plants. Mold on bread is an objectionable variety. Other germs are poisonous, and if we are weak, ill-fed, or have not sufficient oxygen in our blood to destroy these germs when they get into our system, they develop disease. Therefore to avoid them we must breathe plenty of pure air, keep ourselves and our food clean, and keep the air as clean as possible. Ventilation. We can improve the air in our rooms in several ways.

The school kitchen textbook