In selecting food, with reference to health, the following principles must be borne in mind.
First, that there are general rules in regard to healthful food and drink, which have been established, not by a few, but by thousands and thousands of experiments, through many ages, and in an immense variety of circumstances. It is these great principles, which must be the main dependance of every mother and housekeeper, to guide her in selecting healthful food and drinks for her children and family. These rules are furnished by medical writers and practitioners.
Secondly, there are occasional exceptions to these general rules, and when such occur, two errors should be avoided. One is, giving up all confidence in the deductions of a wide experience, established by extensive experiments, and assuming that we have no rules at all, and that every person must follow the guidance of mere appetite, or his own limited experience. The other is, making the exception into a general rule, and maintaining that every person must conform to it.
For example, it is found by general experience, that milk is a very safe and healthful article of food, and that alcoholic drinks are very unhealthful. But there are cases which seem to be exceptions to this rule; for some children never can eat milk without being made sick, and there are cases known where men have lived to a very advanced age and in perfect health, who have daily used alcoholic drinks, even to the point of intoxication.
Still, it is very unwise to throw away the general rule and say, that it is just as well for children to drink alcoholic drinks as to use milk,—and as unwise to claim that every person must give up the use of milk because a few are injured by it.
The true method is, to take the general rules obtained by abundant experience for our guide, and when any exceptions are found, to regard them as exceptions, which do not vacate the general rule, nor make it needful to conform all other cases to this exception.
It will be the object of what follows, to point out the general rules, which are to regulate in the selection of drinks and diet, leaving it to each individual to ascertain, by experiments, what are, and what are not the exceptions.
In the first place, then, it is a general rule that man needs a variety of aliment, so that it is unfavorable to health to be confined to only one kind of food.
The various textures of the human body are composed of chemical compounds, which differ from each other, both as to ingredients, and as to modes of combination. It is true, that every portion of the body may be resolved to a few simple elements, of which oxygen, hydrogen, carbon, and nitrogen are the chief. But the bodily organs have not the power of forming all the various animal tissues from these simple elements. Instead of this, they must be introduced into the body in various complex and different combinations, as they exist in the forms of gluten, fibrine, albumen, caseine, and other animal and vegetable compounds.
Thus the sugar, starch, and oils, found in certain kinds of food, supply the carbon which sustain the combustion ever carried on in the lungs by the process of breathing, and which is the grand source of animal heat. On the contrary, the blood, muscles, skin, cartilages, and other parts of the body, are daily nourished and renewed, some by the gluten contained in wheat, others by the albumen of eggs, others by the caseine of milk, and others by the fibrine of animals. All these are found in a great variety of articles used as food. When received into the stomach, the organs of digestion and assimilation prepare, and then carry them, each to its own appropriate organ, and then the excreting organs throw off the surplus.