These differences in food use, established by long custom, have to be taken into account in all considerations of the world's food supply. They are differences which cannot be easily or quickly changed, even under circumstances which such great emergencies as war may produce. For example, we in America are accustomed to eat corn as food in the form of green corn, corn meal, corn flakes, etc. And in Italy one of the great national dishes is _polenta_ (corn meal cooked in a certain way). But when the Commission for the Relief of Belgium tried to introduce corn as human food in Belgium, because of the large amount that could be obtained from America when wheat and rye were scarce, it met with great opposition and but little success. To the Belgians, corn is food for animals. SCIENTIFIC CONTROL OF FOOD An important point brought out by the war-time food problem is that of the "scientific" make-up of the personal ration. Not only are the national food habits of a people often difficult to understand from a point of view of taste, but they are often of such a character as to lead to a most uneconomical use of food. The exigencies of a world food shortage and a shortage of shipping for food transport have made it necessary for food ministries and relief organizations to give careful consideration to the most economical selection of foods for import and distribution, both from the point of view of economy of space and weight and lack of deterioration during shipping and storage, and from that of concentrated nutritional values and proper balancing of the ration. Food provides energy for bodily work and maintenance. It is the fuel for the human machine. Scientific students of nutrition measure the amount of energy thus provided, or the amount needed by the body, in units termed calories. Physiologists have determined by experiment the different amounts of calories produced by different kinds of foods and the varying amounts needed by men at rest, at light work, at hard work, by women and by children. By analyzing the make-up of a given population as to proportions of men, women and children, and of work done by them, it is possible to express the total food needs of the population in calories and to arrange for the most economical provision of the total calories necessary.