GROWTH AND SENESCENCE 



33 



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140 

 130 

 120 



uo 



100 



90 



80 4 

 70 If 



60 



obtain the oxygen directly from the air by means of its lungs 

 and the food by means of its mouth, stomach, and bowels. 

 This revolutionary change in the mode of nutrition affects but 

 slightly the course of growth. There is a loss of weight for 

 about three days, probably largely due to the fact that the 

 milk flow is not properly established for several days follow- 

 ing parturition, then growth is in full swing again. The in- 

 fantile stage embraces the first 

 two years after birth, that is, 

 up to the time the milk teeth 

 come into place. 



The infant stage is followed 

 by the fourth, or juvenile, 

 stage lasting from about three 

 years up to about twelve years 

 in girls and fourteen years in 

 boys. We have examined a 

 large number of growth curves 

 and have found that during 

 this stage growth in weight 

 proceeds at the constant rate 

 of about 9 per cent per year. 

 Thus, if a child weighs 40 

 pounds, he gains about 9 per 

 cent of 40 or 3.6 pounds per 

 year j if he weighs 70 pounds, the gain is about 9 per cent of 70 

 or 6.3 pounds per year, and so on. The fact of growth at a con- 

 stant rate from 5 to 1 5 years is illustrated in Figure 1 7. 



Then follows the fifth stage, that of adolescence, with the 

 wonderful unfolding of the masculine or feminine person- 

 ality. Overnight the youth is metamorphosed into a man or a 

 woman. 



The advent of the adolescent stage in girls is marked by the 

 appearance of the phenomenon of menstruation, usually ap- 

 pearing between the ages of thirteen and fourteen years, de- 



Age 



Figure 17. Growth of well-nourished chil- 

 dren from 5 to 18 years. In the case of 

 these well-nourished children, growth be- 

 tween 5 and 15 years takes place at a con- 

 stant percentage rate, namely, 9.6 per cent 

 per year, that is, the body weight is doubled 

 once in 7.2 years. In the case of poorly 

 nourished children, the percentage rate of 

 growth is accelerated at the time of puberty. 



