Having the fire well under way the housekeeper turns her attention to the breakfast. A great variety of chemical actions may here be considered. In the first place, why must we -"eat to live ?"
Wherever there is life, there is chemical change; and as a rule a certain degree of heat is necessary in order that chemical charige may occur. Vegetation does not begin in the colder climates until the air becomes warmed by the heat of the spring. When the cold of winter comes upon the land vegetation ceases.
Since many animals live in temperatures in which plants would die, it is evident that they must have some source of heat in themselves. This is found in the union of the oxygen of the air breathed with carbonaceous matter eaten as food and the formation of carbon dioxide and water, just as in the combustion of wood or coal. Only instead of this union taking place in one spot and so rapidly as to be accompanied by light, as in the case of fire, it takes place slowly and continuously in each living cell. Nevertheless, the chemical reaction seems to be identical.
The heat of the human body must be maintained at 98.5 ° F - the vital temperature - the temperature necessary for the best performance of the normal functions. Any continued variation from this degree of heat indicates disease. Especially important is it that there be no considerable lowering of this temperature, for a fall of one degree is dangerous, since in that case the chemical changes necessary to the body cannot be carried out.
The slow combustion or oxidation of the carbon and hydrogen of food cannot take place without an abundance of oxygen; hence the diet of the animal must include fresh air - a point not always considered.
The amount of oxygen taken in by the body daily is equal to the sum of all the other food elements.
The power to do mechanical work comes from the combustion of fuel. The body is a living machine capable of doing work, raising weights, pulling loads, and the like. The animal body also requires fuel in order to do such work as thinking, talking, even worrying. For the present, then, we will say that food is necessary, (I) to preserve the vital temperature and (2) to enable the body-machine to do its work.
Fig. 13. Blue Flame Oil Stove, Showing Oil Reservoir and Lighting Ring
Suppose we begin our breakfast with fruit, say, an orange or a banana. Fruits are especially rich in sugars and these are composed of carbon, hydrogen, and oxygen. If sugar is placed upon a stove, it will melt and steam (water) will pass off into the air, leaving the black charcoal (carbon) on the stove. Moreover, sugars burn easily and fiercely. We shall get both heat and energy from our fruit. Within the body it will be changed into water and carbon dioxide-Fruits contain a large percentage of water; but the banana is capable of giving more energy and heat than the orange, because it has much less water and more sugar. Fruit loses in drying a large portion of its water, so that dried fruits contain a larger percentage of food materials than fresh fruits. For instance, raisins are 60 per cent grape sugar.
Fruits consist of a loose net-work of a woody material holding the soft pulp and this woody fibre, called cellulose, is practically indigestible. Cooking softens this, making cooked fruits easier to digest.