766 THE POPULAR SCIENCE MONTHLY. 



Having thus endeavored to show the extent to which human 

 life may be prolonged, and having examined some of the causes 

 or antecedents of longevity, the last subject for inquiry is the 

 means by which it may be attained. Certain preliminary condi- 

 tions are obviously requisite ; in the first place there must be a 

 sound constitution derived from healthy ancestors, and in the 

 second there must be a freedom from organic disease of important 

 organs. Given an individual who has reached the grand climac- 

 teric, or threescore and ten, and in whom these two conditions 

 are fulfilled, the means best adapted to maintain and prolong 

 his life constitute the question to be solved. It has been said that 

 " he who would long to be an old man must begin early to be one," 

 but very few persons designedly take measures in early life in 

 order that they may live longer than their fellows. 



The whole term of life may be divided into the three main 

 periods of growth and development, of maturity, and of decline. 

 No hard and fast line can be drawn between these two latter 

 phases of existence : the one should pass gradually into the other 

 until the entire picture is changed. Diminished conservative 

 power and the consequent triumph of disintegrating forces are 

 the prominent features of the third period, which begins at differ- 

 ent times in different individuals, its advent being mainly con- 

 trolled by the general course of the preceding years. The "turn- 

 ing period/' also known as the " climacteric " or " middle age/' lies 

 between forty-five and sixty ; the period beyond may be considered 

 as belonging to advanced life or old age. The majority of the 

 changes characteristic of these last stages are easily recognizable. 

 It is hardly necessary to mention the wrinkled skin, the furrowed 

 face, the " crow's feet " beneath the eyes, the stooping gait, and the 

 wasting of the frame. The senses, notably vision and hearing, 

 become less acute ; the power of digestion is lessened ; the force 

 of the heart is diminished ; the lungs are less permeable ; many 

 of the air-cells lose their elasticity and merge into each other, so 

 that there is less breathing surface as well as less power. Si- 

 multaneously with these changes the mind may present signs of 

 enf eeblement ; but in many instances its powers long remain in 

 marked contrast with those of the body. One fact connected with 

 advanced life is too often neglected. It should never be forgotten 

 that while the " forces in use " at that period are easily exhausted, 

 the " forces in reserve " are often so slight as to be unable to meet 

 the smallest demand. In youth, the vires in posse are super- 

 abundant ; in advanced life, they are reduced to a minimum, and 

 in some instances are practically non-existent. The recognition 

 of this difference is an all-important guide in laying -down rules 

 for conduct in old age. 



Jn order to prolong life .and Jit the same time to.enjpy it, occu-: 





