One of the most interesting peculiarities of living things is that they all go through a regular and definite course of changes, forming a cycle, or circle, of development. Sometimes these changes are quite complicated. For instance, from the egg of a butterfly there comes, not a butterfly, but a caterpillar or larva. The caterpillar grows, and at last changes into a pupa (pu’ pa), or resting stage (the chrysalis), and from this chrysalis the new butterfly comes out.
The changes are often much simpler than this; but it is always true that the young of any living thing is different from its parents, and that it goes through a definite series of changes until it arrives at maturity.
Growth and Development.After a child is born, it is weak and helpless, wholly dependent upon its parents.
Then slowly, day by day, week by week, and month by month, it grows in size, weight, strength, and intelligence. It learns to creep and then to walk, to coo and then to speak, and becomes in time an active, romping boy or girl, and finally a full-grown man or woman, in possession of all the powers of maturity.
The average rate of growth in height and weight, calculated from the measurement of a large number of children, is shown in Fig. 79. At birth, as a rule, the baby weighs six or eight pounds and is less than twenty inches long, about one-twentieth of its weight when full grown and less than a third of its final height. By the end of the first six months, the child’s weight has doubled. By the fifth year, he weighs on an average forty pounds, by the tenth year sixty, and by the fifteenth year one hundred pounds. The growth, as you see by the diagram, is very rapid at first, and the per cent of increase grows less and less, as is indicated by the flattening of the curve.
All this time there is going on, not merely an increase in total size, but a great change in the relative size of different parts. Though the body as a whole increases twentyfold in weight from birth to maturity, the muscles of the adult are nearly fifty times the weight of those in the baby, while the heart is only twelve times as big, and the brain less than four times.
Youth, Maturity, Old Age.For the first twenty or thirty years of life, the child and the young man or woman are growing bigger and stronger physically and mentally.
From thirty years to fifty years, the man or woman is in the full prime of mature life and vigor. The wasting away of the body, which goes on all through life, is overbalanced in youth by the growth of new living tissue, but in the prime of life it is about equalized by the building-up process. At forty-five or fifty years of age, the wasting away begins to be greater than the growth. The walls of the blood vessels harden and lose their elasticity, and the kidneys do not work so well as in youth. After this, though the mind may be at its best, the rest of the body is less vigorous, and finally old age comes on.
Hygiene in Relation to Youth and Old Age.Healthful habits are particularly important in youth, because it is during this period that the strength and beauty of the mature body are usually determined. If a child gets poor food or not enough food, he will never grow to full height and strength. If he does not live much in the open air and sleep with windows open, he will be liable to colds and diseases of the lungs and throat. If he does not exercise, his muscles will not grow strong. If he forms the habit of slouching, he will find it hard to carry himself well when he grows up. If he gets into nervous and fretful habits of mind, it will be difficult for him to get out of them in later years.
Just as the habits of youth have much to do with health and happiness in mature life, so the habits of both youth and mature life have much to do with the coming on of old age. Most people grow old too soon. There is an increase year by year in the diseases of adult life. The way to keep well and strong as long as possible is to form and retain habits of healthy living.
Effects of Tobacco on Growth.It is commonly believed that the use of tobacco by boys has a definite effect in stunting growth. Some years ago, Dr. Seaver of Yale made a comparison of the physical development of smokers and non-smokers during the four years they spent at college. He found that the students who did not use tobacco gained 10 per cent more in weight, 24 per cent more in height, 27 per cent more in chest expansion, and 77 per cent more in lung capacity than did the smokers.
It should be remembered, in such a comparison as this, that many things besides smoking may have some effect on the results. For instance, athletes are not allowed to smoke while in training, and being men who lead a healthy outdoor life, are certain to develop well. The boys who smoke in college, on the other hand, are very likely to do other things that will injure their health.
We are quite sure, however, that tobacco affects the digestion, the heart, and the nervous system, particularly when used by young people, and these unfavorable effects naturally react upon growth and development. It is certain, also, that smoking has some effect on “the wind” (really, as we have seen, on the heart) which unfits a boy for athletic success, and that its effect on the nervous system lowers the power of concentrated mental work.
It is for these reasons that most state laws make it a crime to sell or give tobacco to boys under a certain age.
QUESTIONS FOR DISCUSSION AND REVIEW
1. What hatches from the egg of a butterfly? What is the life cycle of a butterfly?
2. Is there any difference, other than size, between a baby and a full-grown man or woman?
3. Look at the curve on page 204 and see what an average boy should weigh at 3 years of age. At 9 years. A girl at 7 years. At 11 years.
4. Where does the child’s body get material from which to grow?
5. What is the difference between the processes going on in the body in youth and in old age?
6. Why is it easier to form good health habits while you are young and growing than after you are full-grown?
7. It is known that smoking injures the digestion, the respiration, and the heart action. What effect would this have on a boy’s growth?