It is remarkable that physiologists and others who were interested in the subject of nutrition, failed for so many years to appreciate evidence so abundant in human experience, that the proper selection of food was a most important means of improving or preserving health. Beri-beri incapacitated many millions of people during the centuries before its cause became known. It certainly occurred in Japan two centuries before the Christian era. It was not, however, until Eijkman, in 1897, compared the effects of different kinds of rice used as human food in Java, on pigeons and poultry, that a clue was gained as to the actual cause of the disease.

It had been appreciated for more than a century by some people that certain fresh fruits and vegetables would effect a cure of scurvy, and that it attacked only those who were restricted for a time to a diet of stale or cooked foods. It was not until after 1900, however, that Hoist brought out clearly through his experiments, on animals, the fact that cooked and dried foods were scorbutic and that fresh vegetables had a most extraordinary power to induce relief of the symptoms of scurvy. The nature of the cause of scurvy could not be discovered by experiments with the rat, since it is not susceptible to this disease. The guinea pig is especially well adapted for this purpose.

Eye lesions varying from mild to distressing nature have been common in several parts of the world for many years. No student of nutrition suspected that there was any cause for these other than infection until the relation of one type to specific starvation for fat-soluble A was established. McCollum and Simmonds showed clearly that the keratomalacia or xerophthalmia which had been observed by several investigators who had restricted rats to faulty diets, was due not primarily to infection, but was of specific dietary origin and results from lack of fat-soluble A. It is, therefore, a symptom of a deficiency syndrome comparable to beri-beri or scurvy. Human diets are always too complex to admit of interpretation as to their deficiencies except on the basis of carefully planned experiments on animals. It was for this reason that it was impossible for the earlier investigators to discover the true causes of the so-called deficiency diseases. Experimental studies with diets composed of purified food substances formed the key to the complete understanding of the natures of the etiological factors in each of these syndromes. Perfecting the biological method for the analysis of a food-stuff, formed the foundation of our knowledge of how to combine our natural foods so as to prepare diets which fall little short of the ideal in their capacity to induce optimal nutrition.

The rapid development in the course of a decade, of a satisfactory understanding of the fundamental principles of nutrition, and the manner in which satisfactory diets can be planned, constitutes one of the greatest triumphs in the whole field of science. To-day the whole subject seems relatively simple, and the student of to-day is likely to forget that but a decade ago, protein content, fuel value and digestibility were the only factors deemed of much importance in the discussion of food.