REPR OD UCTION. 487 



an increase in all dimensions and in weight. In determining the extenl of 

 growth, the two most convenient and mosl commonly used measurements are 



those of length, or height, and weight. For the embryo the following table 

 has been compiled by Hecker : ! 



Table shouting flic Average Length and Wt ight of the Human Embryo at 



Different Ages. 



Month. Length of embryo in centimeters. Weight of embryo in grams. 



Third 4 to 9 11 



Fourth 10 to 17 57 



Fifth 18 to 27 284 



Sixth 28 to 34 634 



Seventh 35 to 38 1218 



Eighth 39 to 41 1569 



Ninth 42 to 44 1971 



Tenth 45 to 47 2334 



The length and the weight at birth vary very greatly. The average measure- 

 ments, as given for over 450 infants in Great Britain, are, for height, males 

 19.5 inches, females 19.3 inches; for weight, males 7.1 pounds, females, 6.9 

 pounds. The weight at birth is said to be greater the nearer the mother's 

 age is to thirty-five years, the greater the weight of the mother, the greater 

 the number of previous pregnancies, and the earlier the appearance of the first 

 menstruation. Race and climate are also of influence. Minot 2 believes that all 

 of these influences work principally through prolonging or abbreviating the 

 period of gestation, and that the variations at birth depend partly upon the 

 duration of gestation and partly upon individual differences of the rate of 

 growth in the uterus. 



Growth of the Body after Birth. — In studying the growth of the body 

 after birth two methods have been employed, named the "generalizing" and 

 the " individualizing " methods. The former consists in deducing the course 

 of growth by averages or other central values from statistics taken from a 

 large number of individuals at different ages. It is the method more com- 

 monly employed ; it shows the course of growth of the typical child, but i- 

 inexact in enabling future growth to be predicted in individual cases. The 

 individualizing method consists in measuring the actual growth of the same 

 individual through successive years; ; t shows well the relation of the indi- 

 vidual to the type throughout the period of growth. The course of growth 

 of British boys and girls from birth up to the age of twenty-four is graphically 

 shown in the accompanying diagram (Fig. 229). Growth is here seen to be 

 rapid during the first live years of life, then slower up to the tenth or 

 the twelfth year. From thence up to the fifteenth or the seventeenth year 

 — that is, preceding and including puberty — marked acceleration occurs, 

 which in turn is followed by slow increase up to the twentieth or the 

 twenty-fifth year. For from live to ten years thereafter slight increase in 



1 C. Heokor : Monatsschrift fur Oeburtskunde mi, I Frauenkrankheiien, 1866, >. wli. 

 • ( '. S. Minot : Human Embryology, I s '. 1 '-!. 



