862 REPRODUCTION, DEVELOPMENT, GROWTH AND DEATH [CH. L1X. 



THE NEW-BORN CHILD AND THE CHANGES IT UNDERGOES 

 AFTER BIRTH. 



The new-born child, which in the uterus was obtaining its 

 nutriment and oxygen from its mother's blood, is severed from the 

 organ called the placenta, by means of which this was accomplished, 

 by cutting through the umbilical cord. The want of oxygen is met 

 by the child beginning to breathe, and its nutriment is supplied by 

 its mother's milk, which later on is supplemented and replaced by 

 other articles of diet. Immediately after birth certain changes 

 occur in the circulatory system; the foramen ovale, the opening 

 between the two auricles, begins to close, and so do the ductus 

 arteriosus and the ductus venosus. The now functionless umbilical 

 vessels close also until they are reduced to mere fibrous cords. 

 These changes are completed in a few days, and the circulation then 

 takes the course it traverses for the rest of life. 



In addition to this there are changes of a more general kind, the 

 most obvious of which is growth; this is accompanied with the 

 completion in the formation of certain organs and tissues which are 

 in a comparatively immature condition when the child is born. 

 Thus medulla tion of the fibres in the central nervous system is 

 taking place, and the process of ossification continues until the 

 bony skeleton is perfected. The generative organs reach maturity 

 at the period of life known as puberty. 



The rate of growth after birth is not so rapid as it is in utero ; 

 and every year the relative increase in size gets less and less. On 

 the average, girls in the earlier years grow more than boys, but at the 

 onset of puberty this relationship is usually reversed. At puberty 

 there is generally an acceleration of the rate of growth in both sexes, 

 but this gradually declines, and finally growth ceases. 



Puberty then is the period at which the sexual organs become 

 matured and functional. In girls this occurs on the average at 

 about fourteen or fifteen years of age, and is marked by the onset of 

 menstruation. Menstruation, or the monthly flow, continues until 

 the age of forty-five to fifty, when it ceases either gradually or 

 suddenly, and after this period (the menopause or climacteric) further 

 production of offspring is not possible. The menopause is usually 

 accompanied with great depression and other disturbances of a 

 physical and mental nature. 



In boys, puberty is usually a little later developed than in girls, 

 but there is no limit at the other end of life corresponding to the 

 menopause. 



In both sexes the onset of puberty is accompanied by the 

 secondary sexual characters becoming pronounced, such as the 

 increase in fullness of the mammary glands in the female, and the 



