GROWTH AND SENESCENCE 



35 



Yp 



«4 



10 23 30 40 50 60 TO 



Age 



clining physical powers in man are usually accompanied by sev- 

 eral external manifestations in the secondary sex characteristics. 

 One of these is an increasing tendency to corpulence after the 

 age of thirty-five. The increasing tendency to fattening in 

 emasculated animals is a well- 

 known phenomenon. Another 

 external sign of declining sex 

 powers is the appearance of 

 coarse hairs on the face and 

 body. Stockard makes the fol- 

 lowing remarks concerning the 

 increased hairiness in man 

 after thirty-five: "On first 

 thought one might consider 

 him to have fully arrived 

 at the completely developed 

 male state. This is not correct, 

 however, since the gonads of 

 such an individual have actu- 

 ally begun to decrease in the 

 sexual power. The coarse hair 

 growth is a plumage expres- 

 sion resulting from a decline 

 in the male gonadial activity 

 rather than the attainment of 

 its zenith." Stockard thinks 

 that the development of the 

 characteristic plumage in the 

 Golden Seabright Bantam 



rooster after castration is comparable to the growth of the coarse 

 hair in man with the decline in his reproductive powers. The 

 reproductive period in man may be considered as practically at 

 an end at the age of sixty. The period between twenty-five and 

 fifty or sixty may, therefore, be considered as the sixth or mid- 

 dle life stage. 



Figure iS. Age changes in the strength of 

 grip. The curves show that we are at our 

 best in this respect between 20 and 30 

 years. 



Aqs 



Figure 19. Age changes in vital (lung) ca- 

 pacity. The curve shows a distinct decline 

 in vital capacity after the age of 30 years. 



