PHASES IN THE LIFE OF THE INDIVIDUAL 675 



than they are in the human species, and have already been 

 mentioned in dealing with the internal ovarian secretions (p. 314). 



SENESCENCE 



As age advances, in addition to the menopause changes 

 which relate more especially to the cessation of the female 

 generative functions, atrophic changes of one sort or another 

 take place in both sexes throughout practically the entire system. 

 The internal spongy structure of the bones is dissolved away, 

 so that they are left with only a hard external shell and conse- 

 quently become brittle. The teeth decay and drop out. The 



FIG. 150. Section through vaginal mucous membrane of woman of 

 sixty-one. (From Sellheim.) 



muscles shrink in volume, the actual fibres of which they are 

 composed becoming smaller in size and fewer in number. The 

 arterial walls lose their elasticity and undergo sclerosis, a 

 characteristic which is so constant that it has given rise to the 

 well-known dictum that " a man is as old as his arteries." The 

 tendons and ligaments also become calcified, and there is a 

 consequent shrinkage of stature. The size of the liver and 

 other viscera undergoes diminution, but the kidney and heart 

 retain their size ; in fact the heart is usually slightly enlarged 

 in old age, but this apparent hypertrophy is not associated 

 with an accession of power but with an increased feebleness, 

 and the pulse, in order to compensate for the weakness of the 

 enlarged heart, beats more quickly, the normal rate of seventy- 



