ward; these form articulations or joints with the neighboring vertebræ. Of the other processes, one projects dorsally and two project laterally; these give attachment to the muscles of the back. The two vertebræ directly beneath the head are modified so as to permit the skull to rest in the upper one; this articulates freely with the second vertebra, thus permitting of the nodding and turning movements of the head. Besides these individual adaptations, the vertebral column, as a whole, is peculiarly adapted to protect the brain from jar; this is seen in the double bend of the vertebral column and the pads of cartilage between the individual vertebræ. The whole column of vertebræ joined each to the other supports the weight of the body. The largest vertebræ at the base are joined to the huge pelvic bones for the better support of the body above. That part of the vertebral column of man which bears the ribs is known as the thoracic region. The ribs, twelve in number, are long, curved bones which combine lightness with strength; joined by elastic cartilage to the sternum in front and to the vertebræ behind, they form a wonderful protection to the organs in the thoracic cavity, and yet allow free movement in breathing.

The Appendages. The parts of the skeleton to which the bones of the anterior and posterior appendages are attached are respectively known as the pectoral girdle (from which hangs the arm) and the pelvic girdle (which joins the leg bones to the axial skeleton).

The bones of the appendages attached to the pectoral and pelvic girdles are adapted peculiarly to locomotion and support; for this purpose the bones are long and strong, hinged by very flexible joints. The latter are especially free in the hand to allow for grasping. In the leg, where weight must be supported as well as carried, the bones are bound more firmly to the axial skeleton. The bones of the foot are so arranged that a springy arch is formed which aids greatly in locomotion.

The Human Skull.

- The skull shows wonderful adaptations for its varied functions. The brain case is compactly built, its arched roof giving strength. The eye and inner ear are protected in sockets of bone.

The skull: F., frontal bone; P., parietal bone; T., temporal bone; SP., sphenoid bone; O., occipital bone; U.J., superior maxillary (upper jaw) bone; L.J., inferior maxillary (lower jaw)

bone.

The lower jaw works upon a hinge, and furnishes attachment for strong muscles which move the jaw.

The skeleton, besides the purposes already described, protects certain organs in the body cavity of man. Other Organs. - We have seen that a body cavity has developed in all animals which are more complex than the baglike hydra, and that a food tube has come to lie within this space. In all such animals the structures which have to do with digestion and absorption of food, most of the structures which have to do with the circulation of this food and of the blood, and organs which give oxygen to the blood, as well as the organs of excretion and of reproduction, lie within the body cavity. These organs we shall discuss in detail later. Nerves. - Other structures, known as nerves, are found in practically all parts of the body. We find that nerves have their endings in the skin, in muscle, and in the cells of glands in various parts of the body; we find a nerve supply to the heart, lungs, and other structures within the body cavity. The most important part of the nervous system in vertebrate animals lies within the cavity formed by bones making up the skull and the vertebral column. This central nervous system, the spinal column and the brain, is a characteristic of the vertebrate animals.

General Functions of the Nervous System. We have seen that, in the simplest of animals, one cell performs the functions necessary to its existence. In the more complex animals, where groups of cells form tissues, each having a different function, a nervous system is developed. The functions of the human nervous system are:

(1) the providing of man with sensation, by means of which he gets in touch with the world about him; (2) the connection of organs in different parts of the body so that they act as a united and harmonious whole; (3) the giving to the human being a will, a provision for thought. Coöperation in word and deed is the end attained. We are all familiar with examples of the coöperation of organs. You see food; the thought comes that it is good to eat; you reach out, take it, raise it to the mouth; the jaws move in response to your will; the food is chewed and swallowed; while digestion and absorption of the food are taking place, the nervous system is still in control. The nervous system also regulates pumping of blood over the body, respiration, secretion of glands, and, indeed, every bodily function. Man is the highest of all animals because of the extreme development of the nervous system. Man is the thinking animal, and as such is master of the earth.

REFERENCE READING FOR THIS AND SUCCEEDING CHAPTERS ON HUMAN BIOLOGY

ELEMENTARY

Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American Book Company.

Davison, The Human Body and Health. American Book Company.

Eddy, General Physiology. American Book Company.

Hall, Elementary Physiology. American Book Company.

Clodd, Primer of Evolution. Longmans, Green, and Company.

Clodd, The Story of Primitive Man. Longmans, Green, and Company.
Ritchie, Human Physiology. World Book Company.

ADVANCED

Halliburton, Kirk's Handbook of Physiology. P. Blakiston's Son and Company.

Hough and Sedgwick, The Human Mechanism. Ginn and Company.

Howell, Physiology, 3d edition. W. B. Saunders Company.

Schafer, Textbook of Physiology. The Macmillan Company.

Stewart, Manual of Physiology. W. B. Saunders Company.
Verworn, General Physiology. The Macmillan Company.

XXIV. FOODS AND DIETARIES

Problem XLII. A study of food values and diets. (Laboratory Manual, Prob. XLII.)

(a) Food values and cost.

(b) Nutritive values as compared with cost.

(c) The family dietary.

(d) Food values.

Why we need Food. We have already defined food as anything that forms material for the growth or repair of the body of a plant or animal, or that furnishes energy for it. The millions of cells of which the body is composed must be given material which will form more living matter or material which can be oxidized to release energy when muscle cells move, or gland cells secrete, or brain cells think. Food, then, not only furnishes our body with material to grow, but also gives us the energy we expend in the acts of walking, running, breathing, and even in thinking.

Nutrients. Certain nutrient materials form the basis of food of both plants and animals. These have been stated to be proteids (such as lean meat, eggs, the gluten of bread), carbohydrates (starches, sugars, gums, etc.), fats and oils (both animal and vegetable), and mineral matter and water. The parts of the human body, be they muscle, blood, nerve, bone, or gristle, are built up from the nutrients in our food.

Proteids. Proteids, in some manner unknown to us, are manufactured in the bodies of green plants. Proteid substances contain the element nitrogen. Hence such foods are called nitrogenous foods. Man must form the protoplasm of his body (that is, the muscles, tendons, nervous system, blood corpuscles, the living parts of the bone and the skin, etc.) from nitrogenous food. Some of this he obtains by eating the flesh of animals, and some he obtains directly from plants (for example, peas and beans). Because of their chemical composition, proteids are considered to

be flesh-forming foods. They are, however, oxidized to release energy if occasion requires it.

Fats and Oils. Fats and oils, both animal and vegetable, are the materials from which the body derives part of its energy. The chemical formula of a fat shows that, compared with other food substances, there is very little oxygen present; hence the greater capacity of this substance for uniting with oxygen. The rapid burning of fat compared with the slower combustion of a piece of meat or a piece of bread illustrates this. A pound of butter releases over twice as much energy to the body as does a pound of sugar or a pound of steak. Human fatty tissue is formed in part from fat eaten, but carbohydrate or even proteid food may be changed and stored in the body as fat.

Carbohydrates. We see that the carbohydrates, like the fats, contain carbon, hydrogen, and oxygen. Here, however, the oxygen and hydrogen are united in the molecule in the same proportion as are hydrogen and oxygen in water. Carbohydrates are essentially energy-producing foods. They are, however, of use in building up or repairing tissue. It is certainly true that in both plants and animals, such foods pass directly, together with foods containing nitrogen, to repair waste in tissues, thus giving the needed proportion of carbon, oxygen, and hydrogen to unite with the nitrogen in forming the protoplasm of the body.

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Inorganic Foods. Water forms a large part of almost every food substance. The human body, by weight, is composed of about 60 per cent water. It is used to make the blood, and a sufficient quantity is most essential to health. When we drink water, we take with it some of the inorganic salts used by the body in the making of bone and in the formation of protoplasm. Sodium chloride (table salt), an important part of the blood, is taken in as a flavoring upon our meats and vegetables. Phosphate of lime and potash are important factors in the formation of bone.

Phosphorus is a necessary substance for the making of living matter, milk, eggs, meat, whole wheat, and dried peas and beans containing small amounts of it. Iron also is an extremely important mineral, for it is used in the building of red blood cells. Meats, eggs, peas and beans, spinach and prunes, are foods containing some iron.

Some other salts, compounds of calcium, magnesium, potassium, and