vii THE STAGES OF LIFE AND DEATH 285 



obtained by selecting individuals free from bodily defects and 

 extending from the average size (50 cm.) of the normal newly- 

 born infant of the white race to that of the strong healthy adult 

 of 25 years of age (man 180, woman 170 cms.). Thus we obtain 

 the total increase in height represented by 130 cms., or 3-6 times 

 the original height. 



According to Quetelet the increase over the size at birth is 

 for the head twofold, the trunk threefold, the arm fourfold, and 

 the leg fivefold, whilst the whole figure attains a height 3f as 

 great as the original. 



As Stratz has pointed out, there is no fixed rule for the annual 

 growth, some children growing quickly, others slowly, and some 

 apparently stopping altogether at certain periods which recur with 

 a certain irregular rhythm. Mulling Hansen's researches tend 

 to show that these great oscillations in growth are reproduced on 

 a smaller scale in the course of the months and weeks and even 

 of the hours of the day. Thus growth in autumn is not the same 

 as in spring ; there are three periods of increase in weight every 

 year, one, from the beginning of August to the middle of 

 December, in which the increase is rapid ; the second, from the 

 middle of December to the end of March, in which the increase 

 proceeds more slowly ; the third, from the beginning of April to 

 the end of July in which it almost ceases. The same alternation, 

 but inverted, is noticeable in increase of stature. Whereas the 

 weight increases by day and decreases during the night, the reverse 

 holds good for the height. The fluctuations are slight (500 grs. 

 10 mms.), but not devoid of importance. 



The Danish pedagogue we have just quoted, who is an adherent 

 of the theory of environment as opposed to that of heredity as a 

 factor in the development of the child, explains these variations 

 by their dependence on the influence of the solar rays, temperature, 

 the alternation of the seasons an influence which is seen in the 

 rhythmic oscillations of growth in vegetable life and also in the 

 animal world. 



The average curves of growth in weight and height, such as 

 those constructed by Pagliani and reproduced in the two upper 

 curves in Fig. 120, show that up to 9 years of age boys are 

 heavier and taller than girls ; during the next four or five years 

 they are smaller, but become taller and heavier again after their 

 fifteenth year. Pagliani attributes this to the fact that growth 

 is very rapid during the two years before puberty and becomes 

 much slower afterwards. Since the age of puberty in women is 

 two to three years earlier than in men, it follows that the period 

 of most rapid growth is earlier in girls than in boys. 



As regards vital capacity and muscular strength, the relative 

 curves, Fig. 120, prove that they are always greater in boys than 

 girls, and the difference increases after puberty. 



