The remarkable researches of Voit, Pettenkofer, Rubner, Atwater, Lusk, Zuntz and Benedict on the metabolism of matter and energy in the body attracted deserved attention and for years occupied a large area in the field of vision of students of nutrition. The researches were extended to the study of some of the finer problems of metabolism. It was shown that carbohydrate can be converted into fat by the tissues, and that a part of the carbon which the protein molecule contains can be converted in the body into glucose. These investigations shed much light on such conditions of perverted metabolism as prevent the oxidation of sugar in the tissues (diabetes). In the light of the new developments in the chemistry of proteins and their digestion products, the amino-acids, Lusk finally explained in great measure, the cause of the specific dynamic action of proteins (4).

It was not until after 1900 that the view began to develop that differences in chemical composition brought forth great differences in the nutritive values of proteins from different sources. Previous to that time it was believed by those who were interested in the nutrition of man and animals, that the results of a chemical analysis were of the greatest importance in showing the nutritive value of any food, and on the basis of such analysis, advice was given as to the manner in which foods should be combined. The chemical methods in use at that time were first described in 1864 by Henneberg, and were adopted by the German Official Agricultural Chemists, and afterwards used by food chemists all over the world.