418 BIOLOGY: GENERAL AND MEDICAL 



a large number of kidneys of various ages, from one year 

 or less up to ninety-nine years, Walsh has found that 

 the proportion of connective tissue between the ducts 

 at the apical portion of the pyramids regularly increases 

 with age. 



The muscular tissues are everywhere atrophic and 

 show a distinct increase of fibrillar tissue, which accounts 

 for the general muscular weakness of the aged. As 

 these changes are not confined to the voluntary muscles, 

 but also affect the cardiac and involuntary muscles, they 

 explain the general cardiac weakness and the inactivity 

 of the alimentary canal. They also explain the tough- 

 ness of the flesh of old animals. The loss of muscular 

 tone is also responsible for the relaxations of the dorsal 

 muscles by which the altered carriage of the aged is 

 partly brought about, and the loss of tone in the abdomi- 

 nal muscles explains the frequency with which umbilical 

 and other herniae occur or enlarge in the aged. 



The bones show pronounced atrophic changes. The 

 anatomical landmarks indicative of muscular attach- 

 ments, etc., well marked in youth, gradually become 

 obliterated and the surfaces smoothed over. The cranial 

 sutures become obliterated and the bones united. The 

 thinner processes of the bones are gradually absorbed. 

 This is perhaps best exemplified by the alveolar proc- 

 esses of the maxillary bones whose atrophy, accompanied 

 by the recession of the gingival tissues from the teeth, is 

 followed by looseness of these organs, which fall out, 

 even if they have not already undergone decay. The 

 loss of the teeth and the absorption of the alveolar proc- 

 esses cause an approximation of the nose and chin, 

 characterized as the "nut-cracker face." In atrophy 

 of the bones the too busy osteoclasts misapply their en- 

 ergy, so that the compact layers become more and more 

 dense and brittle, leaving the cancellous tissue insuf- 

 ficiently supported. Certain portions of the skeleton 

 notably the necks of the femurs also tend to bend. 

 There is also a disposition for bone to form in unusual 



