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The Nature of Foods

BEFORE dealing in detail with the various principles and processes of cookery, it will be well to devote a little space to the nature of foods and the philosophy of feeding. The subject is one of more than theoretical interest, because what is called a practical knowledge must be preceded by some idea of the theory of the work that one is called upon to do, and of the tools employed to do it.

Broadly speaking, food has three purposes to fulfil:--(1) the maintenance of the temperature of the body; (2) the generation of force or energy; and (3) the building up and renewing of the tissues, and repairing the waste which is the inevitable result of tear and wear.

The mechanism of the human machine is in constant operation. Cessation, even for a moment, means death. Even in sleep respiration goes on, and the heart beats with unfailing regularity. All this means work and the expenditure of energy, and requires food in order that it may be maintained. Just as, to make an engine move, you must provide it with a combustible, such as coal, so the human body must be provided with divers aliments in order that it may be kept in good going order. And as the engineer must know something of the internal mechanism of his engine, so should the cook be instructed in the physiology of the human body, in order that he or she may know the effects of different kinds of foodstuffs upon it, and may see that it is neither cloyed nor starved.

The quantity and quality of food required vary, of course, with the age, the climate, the state of health, and the habits of the consumer. Without going into figures, which would probably be misleading, it will be sufficient to say that a young, growing lad needs more food than an old person, and an active man who has much outdoor exercise requires a greater amount of sustenance than one whose occupation is of a sedentary nature. Again, the inhabitants of cold climates, such as the Esquimaux, require a different kind of food from the natives of tropical regions such as the East Indies. But, in order that any kind of food may be beneficial to the human body, it must be transformed into a condition which will enable it to be absorbed into the system. The process by which this is done is called digestion. Far from being a simple process, as many people suppose, digestion is a combination of many different processes, the object of which is to reduce the food into a liquid state. The useful parts are then taken into the blood, while the insoluble and indigestible portions are thrown off by the excreting organs. Thus, we have mastication and salivation (or the mixing of the food with the saliva in the mouth), swallowing, the digestive process which takes place in the stomach, and the action of the bile and various other fluids secreted by special organs. All this presupposes an ordinary state of good health, and thus we see why, in the cases of sick people, of the aged, and of infants, it is necessary to prepare the dishes in such a way as to render them easily assimilable, without casting too heavy a strain on the digestive organs. The infant, as we know, thrives upon milk, which is an almost perfect food; milk, beef-tea, and such like, form the staple of the diet of an invalid; while the aged require their diet to be limited to such articles of food as they can easily digest.

Whatever may be said by faddists, it is certain that man thrives best upon a mixed diet composed of meats, fruits, and vegetables. The ultimate elements of which a man's body is composed must be the same as those contained in his food, but different kinds of foods have different functions to perform. Foods may be divided into two great classes--the inorganic and the organic. The inorganic foods are water and salts. Water is one of the necessaries of life. A person could live without it only a few days. It constitutes by weight three-fifths of the human body, and enters largely into all organic matter. Water is an aid to the performance of many of the functions of the body, holding in solution the various nutritious principles, and also acting as a carrier of waste. It usually contains foreign matter, but the nearer it is to being pure the more valuable it becomes as an agent in the body. Some vegetables, such as vegetable marrow, are almost entirely composed of water. Salts are simply minerals, such as phosphate and carbonate of lime, phosphate and sulphate of potash, phosphate and sulphate of soda, phosphate of magnesia, chloride of potassium, and chloride of sodium. These are distributed in various parts of the human frame. Thus, phosphate of lime is demanded by the bones, phosphate of soda by the cartilages, phosphate of magnesia and phosphate of potash by the muscles. Silica is monopolised by the skin and nails; iron occurs in the colouring matter of the blood, and sulphur exists in the hair. These facts afford valuable guidance in the intelligent drawing up of dietaries. Alkaline salts exist largely in fresh vegetables, and the absence of such articles from daily diet may induce that state of malnutrition which we call scurvy. A deficiency of phosphate of lime in the food of children causes that weakness of the bones which goes by the name of rickets. The organic foods are the most important. They are divided into three groups,--namely, the albuminoids, represented by the white of egg and the lean, or fibrin, of meat; the fats, which contain carbon, hydrogen, and oxygen; and the carbohydrates, which include sugar and starch. The white of egg is composed of albumen, a clear white fluid which solidifies when exposed to a temperature of 108 deg. Fahr., a fact which should be borne in mind by everyone who has occasion to cook an egg. The vegetable world also contributes to this group of foods, for oatmeal, peas, and many vegetables are very rich in albumen. Englishmen, as a rule, eat far too few vegetables. It is quite possible to maintain health on a properly regulated vegetarian diet, although for many reasons it is not desirable. For persons in delicate health or prostrated with illness, vegetables are, as a rule, inadmissible, for they require a longer time to digest, and hence throw too much work on the organs; while a great part of them is thrown off as solid and indigestible matter. The main part, the albuminous--or, as they are sometimes called, the nitrogenous--foods have to play is the building up of waste tissue. It should be noted that the gelatines, of which calf's foot jelly may be taken as a type, belong to this group. Fibrin, in the solid state, constitutes the bundle of minute fibres of which all the muscles of the body are composed. In a liquid state, held in solution in the blood, it also circulates through the system. When found in the vegetable kingdom it is known as gluten. Besides its value as a nutritive constituent of oats, barley, wheat, and other cereals, gluten helps the rising of dough when inflated by carbonic acid gas, and thus renders the bread light and spongy. Casein, which is found in milk, and forms the basis of cheese, is also included among the albuminoids. It differs from fibrin chiefly in containing no phosphorus. The fact that it is the only flesh-forming constituent of milk is a proof of its nutritiveness, and also of its digestibility when in a fluid state.

The next division of the organic foods is constituted by the fats. The fats are obtained from both the animal and vegetable kingdoms, for the oil expressed from the olive and the wax manufactured by the bee are both alike fats. The main object of the fats appears to be to maintain heat. This is effected by a process precisely similar to the combustion of a candle, although in the body it takes place at a much slower rate. The production of heat by combustion is simply due to the chemical act of the combination of oxygen with carbon. This is effected in the body as follows. The carbon, which the blood has extracted from the food, meets in the circulation with the oxygen which the act of inspiration has inhaled from the external air, and the two commingle; and it is a well-known axiom of chemistry that every chemical combination is attended with the production of heat. Lastly, we come to the group known as the carbohydrates, which includes the sugars and starches. It may be mentioned here that starch, before it can be absorbed into the system, has to be converted into sugar. The carbohydrates are almost exclusively confined to the vegetable world. Sugar we get from fruits, but some vegetables--such as the beet--contain large quantities of it. Potatoes, rice, arrowroot, and wheat are also rich in starch, and their nutritive value depends almost entirely on it. The carbohydrates are composed chemically, like the fats, of carbon, hydrogen, and oxygen; but, while doubtless they act as heat-producers, their main function seems to be the evolution of force or energy. The primitive food instincts of man, which nearly always lead him to sound conclusions in the choice of his diet, seem to point to this fact, for while we find the lethargic inhabitants of the Arctic circle existing chiefly on the fat obtained from blubber, we have at the other extreme the lithe and active natives of India, who can undergo great physical strain, supporting life on a diet chiefly composed of the carbohydrates.