Our knowledge of nutrition has progressed hand in hand with the development of the science of Chemistry. Chemical science has given us the clue to an understanding of the nature of the foodstuffs and the changes which take place in digestion, as well as an appreciation of some of the secrets of the metabolic processes which take place within the tissues of the body. Chemistry will continue as time goes on to aid in extending our knowledge of the finer processes of physiology. Nevertheless, it has been possible for a time to advance more rapidly in the study of nutrition, from the theoretical as well as from the practical standpoint, by a systematic feeding of simplified diets to animals, than by means of chemical studies. The results are interpreted on the observations as to the ability or inability of the animals to develop as the diets are modified. Progress has resulted in the past, and will continue in the future to come from the judicious division of labor between the study of food problems by chemical methods and by animal experimentation. In this brief exposition of the present situation respecting our knowledge of foods and nutrition it is desired to present to the reader an appreciation of the viewpoint of an investigator. It will be possible in this way to convey to him an appreciation of the line of reasoning by which the successive steps in the progress of the last few years have been attained. A brief historical account of the researches in this field will serve this purpose. It will, at the same time, illustrate the mental processes of the students engaged in bringing order into this field of scientific inquiry, where before there was no clear understanding.