SENESCENCE IN HIGHER ANIMALS AND MAN 287 



are commonly known as senile atrophy.' They consist essenlially 

 of a decrease in size, with more or less degeneration of cells. These 

 changes are often so extensive and so widely distributed that there 

 is considerable decrease in size and weight of the body as a whole. 



The atrophy may involve to a greater or less extent most or all 

 of the more highly specialized organs of the body, liver, kidneys, 

 alimentary tract, lungs, muscular system, skeleton, and nervous 

 system. The arterial system always shows changes in the direc- 

 tion of decreased elasticity and contractility, and the hardening 

 of the walls known as arteriosclerosis is very commonly present, 

 although some authors maintain that it is not a characteristic 

 feature of old age. The heart often becomes h>pertrophied in- 

 stead of atrophied, but this is believed by many to be a functional 

 reaction to the increased work of the heart in consequence of the 

 changes in the arterial system, rather than a feature of old age. 

 The connective tissue becomes stiffer and harder, but its less 

 highly specialized forms may increase and take the place of more 

 highly specialized organs or tissues which have undergone atroph}-. 

 In connection with these changes of old age the deposition of fatty 

 substances, evidently products of metabolism, occurs in the cells 

 of muscles, liver, brain, and various other tissues. 



The difference in appearance of the spinal ganglion cells of man 

 at birth and in a case of death from old age at ninety-two years are 

 shown in Figs. 115 and 116. In the first figure the young cells 

 have not yet attained their full size, but compared with them, the 

 cells on the left of the second figure are seen by the spaces about 

 them to be greatly shrunken and their cytoplasm contains numerous 

 fat granules stained black by the method of preparation. On the 

 right of Fig. 116 the debris of two cells which have undergone 

 degeneration is seen. 



The atrophy of tissues in old age is manifestly associated with 

 the decrease in rate of metabolism. It is a well-known fact that a 

 decrease or cessation of functional activity in the specialized organs 

 after their development brings about atrophy quite independently 



' For more recent discussions of senile atro[)hy see Bilancioni, '11; DemanRC, '86; 

 Metchnikoff, '03, '10; Minot, '08, chap, ii; Miihlmann, '00, '10; Ribbert, '08; articles 

 in medical dictionaries, cyclopedias, etc. 



