=Vegetable and animal foods.=——It is easy to divide food materials in a general way into those derived from the vegetable kingdom and those derived from the animal kingdom. In the vegetable group we have first, the different parts of many plants, and second, substances manufactured from plants. While we do not usually eat the whole of any one plant, yet there is not any part of the plant that we have not adopted as food. We use roots and tubers in beets, carrots, and potatoes, and the onion is a bulb. In celery and asparagus we eat the plant stalk. Plant leaves give us lettuce and other salads, cabbage and the like. Peas and beans and nuts are seeds, and cauliflower is a part of the flower. The fruit as a whole is familiar in many forms. Manufactured vegetable food materials include flour, meals, breakfast cereals, starch, sugar, molasses and sirups. The animal kingdom gives us the flesh of animals, fish and shell fish, and substances derived from animals, like eggs, milk, and the milk products, cream, butter, and cheese. These materials vary so much in appearance that they would seem to have nothing in common. If, however, we compare the food of different animals and different races of men, we cannot but conclude that this is a mistaken judgment. We find an animal like the lion feeding entirely upon the flesh of other animals, and a strong creature like the ox, eating nothing but grass and grain. We also note that one race of men includes meat in its diet, and another subsists almost entirely upon vegetable food, such as rice and beans. Yet in both cases, these diverse kinds of food accomplish the same end,——body building and the supplying of energy. Let us study two common foods, from the two kingdoms, and see if through this study we can discover in what ways they are alike. =Comparison of milk and beans.=——A moment’s thought enables us to see that in milk we have a food that must have all the elements needed in nutrition, since it is the only food taken by many young animals. The baby and the young calf find in it everything that is needed to build the growing body, and to give them energy. If you see a young calf frisking about the field, you can appreciate how well his food supplies his needs. A simple experiment will help us to find some of the substances contained in milk. Let the milk stand until the cream rises on the top. Skim the cream, warm it slightly and beat it with an egg beater. Butter will soon “come,” and butter, we know, is a form of fat. Warm a pint of the skimmed milk, add to it a dissolved rennet tablet, and set it in a warm place. In a short time, the milk becomes solidified to a consistency like that of jelly. If allowed to stand longer, a watery liquid will separate itself from the solid portion. These are the “curds and whey” that result, also, from the souring of milk. The whey can be squeezed out of the curd, leaving it quite dry. We have now found at least three constituents of milk,——water, fat, and curd.