Dietetics may be defined shortly as the science which treats of foods and feeding. It is to be noted that these words are employed in their most expansive sense to include all alimentary substances which can be or are customarily used by man for nourishing or aiding in the nutrition of his body. As the fundamental object of food is to build up and maintain the body in a condition capable of meeting the demands made upon it by daily life, our first duty will therefore be to obtain an accurate conception of the composition, from a chemical aspect, of the human body, and for the purpose we have in view this need not detain us very long.

This information can, of course, only be derived from analysis of the dead body, and hence we are compelled to surmise that the living material protoplasm of which it is composed is essentially the same substance, dead or alive.

The results of an investigation into the chemical structure of the human body may be stated in two different ways. In the one we may give a detailed account of the various elements of which it is composed, but as few of these exist in the free state this hardly advances our knowledge very materially. It is of some importance to know that the following are always found : carbon, hydrogen, nitrogen, oxygen, sulphur, phosphorus, sodium, potassium, calcium, magnesium, chlorine, iron, iodine, fluorine, silicon, and lithium, the last four being in very small proportions. The other method of stating the composition of the body is of infinitely greater value, because by the grouping of these elements into compounds we actually come face to face with the very substances which require to be built up or renewed by food. Thus we find that at least 70 per cent. of the body weight is composed of water, that the bulk of the remainder consists of proteins and fats, whilst only a very small quantity of mineral matter and still less of carbohydrates are able to be discovered.

The Alimentary Principles

It will seem that these five substances are easily divisible into two classes: the organic, consisting of proteins, fats, and carbohydrates, and the inorganic, including water and mineral salts. The term usually applied to the whole group when referring to their presence in the body is that of the proximate principles, but as component parts of the food they are more generally known as the alimentary principles.

Before concentrating our attention more definitely on these words or making any attempt to give a definition of food, and in order to infuse a real live interest into what may very well become a somewhat dry subject, I think it will be judicious at this stage to give a short, succinct account of the recent controversy on the respective merits of white and brown bread. By this means we shall at once put ourselves in possession of some of the most prominent factors in the domain of dietetics, and at the same time rescue this little treatise from the accusation of being simply an epitome of a dry-as-dust scientific text-book.