858 THE PHASES OF LIFE. 



twelfth year, and the second permanent molars are cut about the twelfth or 

 thirteenth year. There is then a long pause, the third or wisdom tooth not 

 making its appearance till the seventeenth, or even twenty-fifth year, or in 

 some cases not appearing at all. 



810. Shortly after the conclusion of the permanent dentition (the 

 wisdom teeth excepted) the occurrence of puberty marks the beginning of a 

 new phase of life ; and the difference between the sexes, hitherto merely 

 potential, now becomes functional. In both sexes the maturation of the 

 generative organs is accompanied by the well-known changes in the body at 

 large ; but the events are much more characteristic in the typical female 

 than in the aberrant male. Though in the boy, the breaking of the voice 

 and the rapid growth of the beard which accompany the appearance of act- 

 ive spermatozoa, are striking features, yet they are, after all, superficial. 

 The curves of his increasing weight and height, and of the other events of 

 his economy, pursue for a while longer an unchanged course ; the boy does 

 not become a man till some years after puberty ; and the decline of his 

 functional manhood is so gradual that frequently it ceases only when disease 

 puts an end to a ripe old age. With the occurrence of menstruation, on the 

 other hand, at from thirteen to seventeen years of age, the girl almost at 

 once becomes a woman, and her functional womanhood ceases suddenly at 

 the climacteric in the fifth decennium. During the whole of the childbear- 

 ing period her organism is in a comparatively stationary condition. While 

 before the age of puberty, up to about the eleventh or twelfth year, the girl 

 is lighter and shorter than the boy of the same age, in the next few years 

 her rate of growth exceeds his ; but she has then nearly reached her maxi- 

 mum, while he continues to grow. Her curve of weight from the nineteenth 

 year onward to the climacteric remains stationary, being followed subse- 

 quently by a late increase, so that while the man reaches his maximum of 

 weight at about forty, the woman is at her greatest weight about fifty. 



811. Of the statical differences of sex, some, such as the formation 

 of the pelvis and the costal mechanism of respiration, are directly connected 

 with the act of childbearing, while others have only an indirect relation to 

 that duty ; and indications, at least, of nearly all the characteristic differ- 

 ences are seen at birth. The baby boy is heavier and taller than the baby 

 girl, and the maiden of five breathes with her ribs in the same way as does 

 the matron of forty. The woman is lighter and shorter than the man, the 

 limits in the case of the former being from 1.444 to 1.740 metres of height, 

 and from 39.8 to 93.8 kilos of weight, in the latter from 1.467 to 1.890 of 

 height, and from 49.1 to 98.5 kilos of weight. The muscular system and 

 skeleton are both absolutely and relatively less in woman, and her brain is 

 lighter and smaller than that of man, being about 1272 grammes to 1424. 

 Her metabolism, as measured by the respiratory and urinary excreta, is also 

 not only absolutely but relatively to the body-weight less, and her blood is 

 not only less in quantity, but also of lighter specific gravity, and contains a 

 smaller proportion of red corpuscles. Her strength is to that of man as 

 about 5 to 9, and the relative length of her step as 1000 to 1157. 



812. From birth onward (and indeed from early intra-uterine life) the 

 increment of growth progressively diminishes. At last a point is reached at 

 which the curve cuts the abscissa line, and the increment becomes a decre- 

 ment. After the culmination of manhood at forty and of womanhood at the 

 climacteric, the prime of life declines into old age. The metabolic activity 

 of the body, which at first was sufficient not only to cover the daily waste, 

 but to add new material, later on is able only to meet the daily wants, and 

 at last is too imperfect even to sustain in its entirety the existing frame. 

 Neither as regards vigor and functional capacity, nor as regards weight and 



