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FOOD

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make good the constant loss that occurs in all living beings. It stands to reason that the food, in order completely to nourish the body, must contain all the chemical elements of which that body is composed. These chemical elements are carbon, hydrogen, oxygen, nitrogen, sulphur, phosphorus and various other elements in very minute quantities. It will be seen, therefore, that proteid substance in some form must be a part of the food, in order to supply nitrogen, since carbohydrates and fats contain only carbon, hydrogen and oxygen. Milk and eggs are good examples of complete foods. For physiological reasons a mixed diet is best. Green plants, unlike animals, are able to make use of compounds like water and carbon-dioxide, and, by means of the energy derived from the sun's rays, build these into carbohydrates, as starch and sugars. These may be used in conjunction with nitrates to manufacture their protoplasm, which is endowed with life. The construction of starch etc. requires energy, and, by the well-known law of conservation of energy, the sub-stance^ thus formed are endowed with potential energy. The agent that enables plants to utilize the energy from the sun, is their green coloring matter (chlorophyll). Animals must start with complex substances already endowed with energy, and, therefore, require carbohydrates, fats and proteids. The food is the source of energy to the animal-body. See BREAD, BUTTER, FLOUR, MILK, etc.

Food, of plants, consists of materials suitable to be used, without the expenditure of much work upon them, for the formation and repair of the plant-body. Foods for plants therefore are essentially the same as for animals, which is to be expected because the protoplasm is alike in the two. The food of green plants is not different from that of others, but they alone have the power to make food in the green cells under the action of light. (See PHOTOSYNTHESIS.) No other living things possess this power; hence the world is dependent on green plants for its food and for all the fuel whose energy drives its machinery. Carbon-dioxide and water are not properly called plant-food, being the material out of which some foods only are made.

Fool. See JESTER.

Foot, the part of the limb upon which an animal stands when resting. A comparison of the foot in various animals brings out many interesting modifications. The limbs are composed of corresponding parts, but there is great variation as to the development and the number of parts in contact with the earth. In the human foot we distinguish the ankle or tarsus, the instep or metatarsus and the toes or phalanges. The heel rests upon the earth, and this condition is called a plantigrade foot. Other animals,

like the cat and dog, walk on the toes or digits, giving a digitigrade foot. The heel is up in the air and the instep is lifted away from the earth. In deer, cattle, horses and other animals the elevation of the heel has been carried further, and the

animal stands on the tip-end of a single toe; the heel, instep and digits are away from the earth, the tip-end of one only being in con-tact. These points are illustrated in the diagram; in this comparison of the hind limb of man, dog and horse the heel-bone, to which is attached the tendon of Achilles, forms a landmark. It, of course, is to be understood that the fore limbs of dog and horse have undergone similar modifications. The deer, cattle and other animals have an even number of toes, while the elephant with five, the rhinoceros with three and the horse with one are odd-toed. The horse has the most remarkable example of a modified foot; not only are the heel and instep off the earth, but the bones of the instep have become reduced to one, and the animal walks upon the tip of a single toe on each foot of the four feet. It has been shown by fossils in the rocks that the horse's foot has been derived from that of an original five-toed ancestor, by suppression and consolidation of parts. The geological history of these changes extends over more than two million years. (See EVOLUTION.) The word foot is also applied in zoology to the tube-feet of starfishes, the part of the body upon which snails and clams rest, the feet of Crustacea, insects, etc.

Foot'foall, an outdoor game of several varieties, played with a round or oval, inflated ball about 27 or 28 inches in circumference. The ball consists of a rubber bladder encased in a leather cover. The game is a very old one, and now has three main varieties: association-football, which is played extensively throughout the British empire; Rugby football, which originated at Rugby School, England; and American college-football, which is a local development of the Rugby game.

A form of Rugby football was introduced at Harvard University about 1870. It was soon taken up as an intercollegiate game, the rules altered from time to time by those meeting in the intercollegiate football conventions, and the distinctively American

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