It is not so many years ago that students of nutrition were told that a perfect diet must include at least sufficient protein to replace that which was consumed by the life processes of the body, and energy-furnishing substances (carbohydrate and fat), as well as sodium, calcium, potassium, magnesium, iron, sulphur, phosphorus and chlorin. The latter substances, except sulphur, could be taken in as inorganic salts.
When, however, it became possible through the advances in physiologicochemical methods to obtain sufficient amounts of purified proteins and amino-acids, feeding experiments were begun to ascertain, if possible, the relative biologic value of various dietary constituents. Analysis of diet by biologic methods (feeding experiments) soon showed that the foregoing food constituents were not in themselves sufficient to maintain life and function in the animal body.
For many years the attention of physicians had been directed toward diet as a factor in the production of