1018 THE PHYSIOLOGY OF REPRODUCTION. 



that the rate of growth decreases from birth to old age, although not 

 uniformly. At the pubertal period and at other times its downward 

 tendency may be arrested for a time. But, speaking generally, the 

 maximum rate of growth is reached some time during the intra- 

 uterine period, and after birth the curve falls steadily. Senescence 

 has begun to appear at the time we are born.* Thus, according to 

 the statistics of Quetelet, the average male child weighs at birth 6J 

 pounds. At the end of the first year it weighs 18 % pounds, a gain of 

 12 pounds. At the end of the second year it weighs 23 pounds, a 

 gain of only 4-J pounds, and so on, the rate of increase falling rap- 

 idly with advancing years. Jackson f has published an interesting 

 series of observations upon the relative and absolute growth of 

 the human fetus and its different organs during the intra-uterine 

 period. Relative growth is defined as the " ratio of the gain 

 during a given period to the weight at the beginning of the period." 

 From this standpoint he finds that the maximum rate of growth 

 occurs during the first month of fetal life. As determined by 

 the volume of the fetus the ovum increases more than 10,000 

 times in size during this period. In the succeeding months of 

 intra-uterine life the relative monthly growth rate may be expressed 

 by the figures 74, 11, 1.75, .82, .67, .50, .47, .45. During this period 

 the absolute weight is, of course, increasing rapidly, and according 

 to Jackson's observations the total weight of the embryo may be 



calculated at any time from the formula weight (g) =( - ' \ 



\ 6i ) 



Friedenthal t gives the following figures for the growth of the 

 fetus, including the membranes and placenta: 



AGE IN -TTT /-. ABSOLUTE INCREASE PERCENTAGE IN- 



DAYB. CjM8> PER DAY (QMS.). CREASE PER DAY. 



0.000004 



8 0.03 0.0037 90,000 



17 0.86 0.092 307 



20 1.4 0.18 16 



26 2.0 0.1 6 



35 2.9 0.1 4.5 



40 19.0 3.2 29 



60 220.0 10.0 8.4 



100 800.0 14.5 3.0 



120 1200.0 20.0 2.0 



196 2800.0 21.0 1.1 



250 3800.0 19.0 0.6 



280 4500.0 23.0 0.5 



The statistics of extra-uterine growth have been collected and 

 tabulated with great care by a number of observers; for this 



* See Minot, "Journal of Physiology," 12, 97. 



t Jackson, "The American Journal of Anatomy," 9, 119, 1909. 



I Friedenthal, "Physiologic d. Menschenwachstums," 1914. 



