670 THE HUMAN BODY. 



tives in any case are, however, not drugs, but an avoidance of 

 too warm and soft a bed, plenty of muscular exercise, and 

 keeping out of the way of anything likely to excite the sexual 

 instincts. 



In the woman the pelvis enlarges considerably at puberty, 



and, commonly, more subcutaneous adipose tissue develops 



over the Body generally, but especially on the breasts and hips ; 



consequently the contours become more rounded. The exter- 



al generative organs increase in size, and the clitoris and 



^phae become erectile. The uterus grows considerably, the 

 tes enlarge, some Graafian follicles ripen, and menstruation 



mences. 



The Stages of Life. Starting from the ovum each human 

 being, apart from accident or disease, runs through a life-cycle 

 which terminates on the average after a course of from 75 to 

 80 years. The earliest years are marked not only by rapid 

 growth but by differentiating growth or development ; then 

 comes a more stationary period, and finally one of degenera- 

 tion. The life of various tissues and of many organs is not, 

 however, coextensive with that of the individual. During life 

 all the formed elements of the Body are constantly being 

 broken down and removed; either molecularly (i.e., bit by bit 

 while the general size and form of the cell or fibre remains 

 unaltered), or in mass, as when hairs and the cuticle are shed. 

 The life of many organs, also, does not extend from birth to 

 death, at least in a functionally active state. At the former 

 period numerous bones are represented mainly by cartilage. 

 The pancreas has not attained its full development; and some 

 of the sense-organs seem to be in the same case; at least new- 

 born infants appear to hear very imperfectly. The reproductive 

 organs only attain full development at puberty, and degenerate 

 and lose all or much of their functional importance as years ac- 

 cumulate. Certain organs have even a still shorter range of 

 physiological life ; the thymus, for example, attains its fullest 

 development at the end of the second year and then gradually 

 dwindles away, so that in the adult scarcely a trace of it is to 

 be found. The milk-teeth are shed in childhood, and their 

 so-called permanent successors rarely last to ripe old age. 



During early life the Body increases in mass, at first very 

 rapidly, and then more slowly, till the full size is attained, 

 except that girls make a sudden advance in this respect at 

 puberty. Henceforth the woman's weight (excluding excep- 



