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Show why we behave like human beings I Br GEORGE DO USSY. Ph. D. IX. D, ' ...... ...... ........... ..T Why Walking Is More Restful Than Standing IN WALKING, each leg rests half 1 the time. We lire-standing because be-cause neither leg gets rested. The shoulder muscles wblot hold the bead erect also acba from the strain In standing. As we nap la a chair the head nods. Flat feet are not due to a giving way of ligaments; ligaments limit Joint movement Feet become "flat" when the muscles of the arcb fall to support It ; the arch breaks down. The result Is a mld-tarsol joint This Is most likely to happen in long, narrow feet Short feet and high Insteps go with large calves. To raise our body on our toes, we lift our beel. The toes are the fulcrum, the power Is tlie calf muscles; the weight falls on the foot at the ankle Joint but nearest the power at the beet Hence the greater need for large calf muscles. But small calves go with long heel bones. As the foot Is a lever of the second order, the long beel brings the weight nearer the fulcrum that Is, the toes. Henee "flat-foots" do not step off their toes; the fallen arch destroys the lever of the foot ' We nod our head between skull and first vertebrae, or atlas; rotate, between be-tween stlns and second vertebrae, or ails. Both movements are limited by ligaments; otherwise tba signal cord would be crushed. The main business of the face Is to bold the teeth-bearing jaws; eyes and nose moved In by accident The Infant's In-fant's face and neck seem small because be-cause the brain la so large. Their real growth begins with the eruption of the teeth. The skull Is a fulcrum for the Jaw muscles tn chewing. Muscles to bold the fulcrum steady develop with the teeth. The neck grows larger. With the teeth all in place the neck reaches normal sire, the rounded "baby-face" disappears; strong Jaws, powerful muscles, and prominences and ridges on bones of face and bead support the muscles of mastication. The tiny mastoid processes below the Infant's ears become adult structures as big as thumbs, required for muscle support The first or milk, teeth should be in place by the end of the second year. Meanwhile the transverse ridges in the roof of the Infant's mouth disappear. The permanent dentition begins with the first molars In the seventh year; Incisors In the eighth and ninth ; premolars In the tenth and eleventh ; canine and second molars tn tha thirteenth to fourteenth; third molars, or wisdom teeth, in the seventeenth seven-teenth to fortieth year. Startling changes of far-reaching consequence mark the years of adolescence adoles-cence for both sexes. As these changes ere both physical and mental, and as they proceed under impulses from the gonads acting as glands of Internal secretion, they will be described de-scribed In the chapter devoted to the endocrine organs. After maturity the body's chief task Is to maintain its equilibrium: produce pro-duce enough energy and best to keep np repairs and carry on. But from ovum to death, the body never ceases to change. Old age or senile changes precede natural death. These appear toward the end of a span of life which varies tn different species. This s.ian of life for some Invertebrates is less than 100 hours; for some Insects, 17 years; for some fishes and reptiles, over WO yetirs; for some birds and mammals, 120 years. Longevity Is not as 'Welsmann claimed, related to size of body. Some mammals live less than two years, j some locusts seventeen. A dog Is old at 20. I have seen a parrot 117 years old; If matured In Its first year. A tortoise can live 850 years. ' No elephant ele-phant known has exceeded 130 years. Nor does denth "nuturally" follow the reproductive stage; Innumerable animals ani-mals long survive their sex life. But every animal must reach sex maturity ma-turity or its kind dies with It Old age Is decrepliude; the body Is worn out. The mechanism the Infant acquired to walk with breaks down. The spine IS not so supple, the cartilage disks between vertebrae shrink. This decreases stature as much as three Inrhes after fifty. The spine both collapses and "'stoops with age." The knees are bent the hip Joints stiff. The muscles shrink. The body loses Its natural fat Folds of skin appear on neck and face. Tbe toothless Jnws atrophy and the mouth loses its shape. Cheeks and temples cave In. The brain loses weight In the Inst 40 years of life as much aa three ounces. The heart Is enlsrged from over-action to keep the blood coursing through thick, hard arteries. The pulse mounts again. It waa 134 at birth, 110 at the end of the first year, 72 at twenty-one. After eighty. It Is 80. The lungs lose their elasticity, the walls become thicker. Msny women after fifty show a thicker neck, hair on the face, deeper-toned deeper-toned voice, more prominent cheekbones, cheek-bones, ridges over the eyes. Their "feminine"-" traits are less feminine. It Is as though the Inactivity of the gonads pemiltted a retnrn to' a neutral neu-tral condition, halfway between male and female. Old age, senility, decrepitude; the body Is worn out It can no longer function. Death. j by Gcorgt A. DwMT.) |