The reasons for much of the undernourishment among people in this country to-day are to be found in certain widespread misconceptions of long standing as to what constitutes a state of good nutrition or malnutrition and the value and purposes of different foodstuffs. For malnutrition does not necessarily describe a simple condition due to an insufficient amount of food, but to any one of several complex conditions due to a lack in the food of one or more essential substances. One may eat a large amount of food and even have a well-padded body and yet be seriously in need of certain food factors—in other words, be incompletely nourished in some particular. That was possibly the first misconception—the belief that one simply needed enough food, and accordingly was well nourished if three large meals were eaten daily, irrespective of the composition of those meals. A step forward was taken when housewives and people generally accepted the fact that quantity alone was not enough to consider in providing food, but that the dietary should consist of balanced amounts of the five food materials: fats, carbohydrates, proteins, minerals and water, in order to build and maintain the body in a state of health. But this, too, was found to be an error, in so far as it was only a part of the truth, for it was next ascertained that even provision for a suitable balance of the five food groups was not enough to nourish us, but that we must consider the heat-and-energy-producing properties of these component parts, as measured by the caloric unit, and that we must daily take in the requisite number of calories if we would keep our engines going. It is now known that even this is not enough, for we may eat food in ample quantities, consisting of the properly balanced fats, proteins, carbohydrates, minerals and water, and it may daily yield the required number of calories, and still we may suffer from seriously faulty nutrition. We find an explanation for this fact in the comparatively recent recognition of three substances, as yet not clearly understood, which are contained in a certain few articles of food, each one of which is essential to growth and normal health and well-being, though not necessarily concerned in the production of heat or energy. Various terms have been applied to these mysterious, but necessary substances, such as _vitamines_, _accessory food substances_, as applied to all, or fat-soluble A, water-soluble B and water-soluble C to designate them separately. A surprisingly small amount of each of these substances is sufficient to meet the needs of an individual, but no one of these, even in this small amount, can be safely dispensed with, for if the diet is deficient, or lacking in one or more of them some form of nutritional disturbance will result. It may be severe enough to be diagnosed as a disease, or it may be only enough to keep the individual below a normal state of health.