As a general rule, the protein of meat and fish is more completely and more quickly digested than the protein in vegetable foods. The reason is that the vegetable protein is found in cells which are protected by the indigestible cellulose which covers each cell. This covering is not always broken and then the digestive juices are practically powerless. The legumes, which are rich in protein, are comparatively hard to digest. If properly prepared and eaten, they give little or no trouble, but they are generally cooked soft and the mastication is slighted. The result is fermentation. Beans, peas and lentils should be very well chewed, and eaten in moderation, for they are rich both in starch and protein. Nuts are as a rule not as completely digested as meats and animal fats, and the principal reason is that they are eaten too rapidly and masticated too little. Nuts properly masticated, taken in correct combinations and amounts agree very well. It is not necessary, as many believe, to salt them in order to prevent indigestion. In the following pages will be found a number of diet tables, giving compositions and fuel values of various foods which have been grouped for the sake of convenience, for the foods in each group are quite similar. These tables are not complete, for to list every food would take too much space. I have simply selected a representative list from the various classes of foods. Under flesh are given fish, meats and eggs. Under succulent vegetables are given both root and top vegetables, because of their similarity. Nuts, cereals, legumes, tubers and fruits are each grouped because it is easy to gain an understanding of them in this way. Milk is given a rather long chapter of its own because of its great importance in the morning of life. Allow me to repeat that it is impossible to figure out the calories in a given amount of food and then give enough food to furnish so many calories and thus obtain good results. I have already given the key to the amount of food to eat, and it is the only kind of key that works well. However, it is very helpful to have a knowledge of food values. The calorie is the unit of heat, and heat is convertible into energy. A calorie is the heat required to raise the temperature of one kilogram of water one degree C. To translate into common terms, it is the heat required to raise one pound of water four degrees F. One pound of protein produces 1,860 calories. One pound of sugar produces 1,860 calories. One pound of starch produces 1,860 calories. One pound of oil or fat produces 4,220 calories.