454 REPRODUCTION AND DEVELOPMENT 



i. 



and (as when one wrongly tries to compare the values of men with those 

 of women) one finds comparison therefore between maturity, childhood, 

 and old-age more or less illogical except in terms of bodily strength and 

 the somatic functions. These latter maturity exhibits at their best, but 

 no one should fail to see the more substantial compensations of the life- 

 period which follows it in a portion at least of the individuals who are 

 born. . 



Old-age is 'the fourth period of the epochal differences which we need 

 to consider and the last. How, physiologically, does it differ from 

 the. average status of maturity? We may in a word suggest all these 

 differences (save as has just been mentioned) by the term decline, "a 

 bending-downward" toward death, a general weakening of an inherently 

 limited organism. In the preeminent respects above suggested, then, 

 senescence is a superior condition, but in most regards it is the inevitable 

 decay of the " unremaining glory of things that soon are old/' 



The weight and stature both are regularly less in old-age than in the 

 epoch of maturity. 



The causes of the slowly progressive decrease in weight are chiefly 

 the lessening of the water-content of the skeleton; the disappearance of 

 the fat from the body generally, but especially from the muscles; the 

 skrinkage of the muscles (and glands?) from their relative disuse; and 

 the weakness of the nutritive process, making now the growth-balance 

 negative instead of positive, as in childhood, or zero, as in middle-life. 

 Fat represents especially the storage of nutritive tissue, and in old age, 

 unless the digestion be unusually vigorous, this surplus is not produced 

 and stored. The bones become more brittle as age advances: they 

 lose water, collagen, and fat, and become more calcareous. 



The reasons why the aged body is less in size than that of middle-age 

 are in part those just cited as explaining the loss in weight. The stature 

 is less because of the shrinkage of the interosseous cartilages generally, 

 and especially of those between the vertebrae. These plaques lose 

 collagen and chondrigen and in so doing become both thinned and less 

 elastic. In persons accustomed to much manual labor that requires a 

 stooping posture the spinal column has acquired a dorsal bend which 

 further decreases the stature. 



Nutrition in old-age shows the most fundamental differences belonging 

 to this epoch. In no one respect especially, but in all of them, the assimi- 

 lative process has degenerated. Mastication is imperfect because few or 

 many of the teeth are gone or broken. Digestion is defective partly 

 because the alimentary movements are weakened with the other muscular 

 activities and partly because the digestive liquids have no longer their 

 former abundance or (probably) strength. It seems likely that the 

 failing power of mastication is the more important of these deficiencies, 

 although the muscular atonicity of the gut must be also a weighty factor, 

 for we see much harm coming from constipation. 



The chemical defects if any in the digestion, absorption, assimilation, 

 and excretion incident to old-age are not as yet well known. Habit 



