REPRODUCTION. 489 



others in both weight and stature. Beyer 1 has shown that systematic exercise 

 may markedly increase both height and weight. Disease may alter the form 

 of the curve of growth. But the final result seems to depend less upon 

 external conditions than upon race and sex. As an interesting accessory 

 fact it was found by Porter 2 that well-developed children take a higher rank 

 in school than less-developed children of the same age. Tf the percentage 

 annual increase of the total weight he computed, it is found to diminish 

 throughout life, very rapidly during the first two or three years, later more 

 slowly and with minor variations of increase and decrease ; that is, as growth 

 proceeds and the powers of the individual mature, the power to grow becomes 

 rapidly less. This is a peculiar and most interesting fact, and has not been 

 explained. It would seem to signify that the sum of the vital powers 

 declines from birth onward. Many facts indicate that the common concep- 

 tion, dating from the time of Aristotle, of human life as consisting of the 

 three periods of rise, maturity, and decline, must give way to a more rational 

 idea of a steady decline from birth. 



Puberty. — By puberty is meant the period of sexual maturity, at which 

 the individual becomes able to reproduce. In the male the exact time of its 

 onset, characterized primarily by the appearance of fully ripe spermatozoa, is 

 not well known, but is believed to be about one year later than in the female. 

 In temperate climates, therefore, it usually appears in boys not before the age 

 of fifteen ; it is earlier in warmer regions. It is preceded and accompanied by 

 acceleration in bodily growth, already spoken of. Other bodily changes, such 

 as general maturation of the functions of the reproductive organs, alterations in 

 the bodily proportions, increase of strength, and growth of the beard, all of which 

 are elements of the transformation from boyhood to manhood, either occur at 

 that time or follow soon after. One of the most obvious external change- i- 

 that of the voice. Its tone may fall permanently an octave, and for the time being 

 become rough, broken, and uncontrollable. This is due to a rapid general 

 enlargement of the laryngeal cartilages and a lengthening of the vocal cords. 



In the girl the oncoming of puberty is marked more exactly than in the 

 boy by the appearance of menstruation, in the majority of girls in temperate 

 climates at the a«;e of fourteen to seventeen, lint other characteristic anatoin- 

 ical and physiological changes in the body occur. The uterus, the external 

 reproductive organs, and the breasts become larger, while the pelvis widen-. 

 The prepubertal acceleration of growth has been mentioned. Nervous disor- 

 ders are especially prone to make their appearance at this time. The subcuta- 

 neous layer of adipose tissue develops and confers upon the outlines the grace- 

 ful curves characteristic of the woman's body. The mental faculties mature, 

 and the girl becomes a woman earlier and more rapidly than the boy a man. 



1 II. G. Beyer: "The Influence of Kxercise on Growth," Journal of Experimental Medicine, 

 189(i, i. p. 546. See also "The Growth of U.S. Naval Cadets," Proceedings of the United States 

 Naval Institute, 1895, xxi. p. 297. 



2 W. T. Porter: "The Physical Basis of Precocity and Dulness," Transactions of the Acad- 

 emy of Science of St. Louis, 1893, vi., No. 7. See also "The Growth of St Louis Children," 

 Ibid., 1894, vi. No. 12. 



