ic6 HORSE-BACK RIDING. 



result of long observation — the ages are divided into 

 four series : First infancy, from birth to the age of 

 10 years ; second infancy, or adolescence, from lo to 

 20 years. First youth, from 20 to 30 years ; second 

 youth, from 30 to 40. First manhood, from 40 to 55 

 years ; second manhood, from 55 to 70. First old 

 age, from 70 to 85 ; second old age, from 85 to 

 death. 



Flourens prolongs the period of adolescence to 20 

 years, because at that time the development of the 

 bones is completed, and, as a natural consequence, 

 the growth of the body in length. If he extends 

 youth to 40 years, it is because at that age the body 

 attains its final size, whatever it gains afterwards 

 being only an accumulation of fat. Then if he pro- 

 longs manhood to 70 years, it is because he perceives 

 a work of invigoration, which renders every part of 

 the body stronger and more complete — which work 

 begins at 40 to 55 years, and continues nearly to the 

 age of 70. 



Old age then commences. According to this 

 author, its characteristic is the loss of strength in 

 reserve ; there remains for the old man the active 

 power only, that of the moment. 



Two celebrated physiologists, Haller and Hufeland, 

 had already, prior to the researches of Flourens, 

 opened a vast perspective to this desire for longevity, 

 which is one of the weaknesses of mankind. Haller 

 sought to estimate the natural length of human life, 



