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CELLS, TISSUES, AND ORGANISMS 



f ■■ 



SOJahre 



Figure 1. Concentration of 

 cholesterol and of calcium in 

 the human aorta at different 

 ages. (From Blii-ger, 1939.) 



the amount of cholesterol per 100 grams of dry aorta progressively in- 

 creases some five- or six-fold; the increase m caicium is, even greater. 

 \\^e label these changes "aging" rather than growth primarily because 

 we do not like the result. We say this is an expression of atherosclerosis, 

 but the general trend can scarcely be called a "disease," since it occurs 

 in all people, though the rate of progression varies. 



Because age changes do not proceed at the same rate in different 

 individuals, refuge is taken in the concept of "physiological age," 

 which, replacing chronological age, presumably makes all individuals 

 conform to some universal aging curve. But what, then, is the measure 

 of physiological age? Scores or hundreds of measures may be pro- 

 posed; even if they are normalized to 'give equal answers for the aver- 

 age person, they will give diflFerent answers when individuals are com- 

 pared. One man may be relatively young in muscular strength, middle- 

 aged in vision and in his arteries, old in his joints, and senile mentally. 

 Or the other way around. Any combination of youthful and aged at- 

 tributes may be found. 



Except as a scientific problem, aging per se may not bother us so 

 much. Some loss in physical strength and speed in exchange for a gain 

 in accumulated knowledge and wisdom would not be outrageous. What 

 concerns us more are the real disabilities of illness that too often ac- 

 company aging. For this reason, and because we know so little of the 

 basic processes of aging, a discussion of aging generally turns out to 

 be either mere description of age changes, as in the aorta data in Fig- 



