CENTRAL NERVOUS SYSTEM. 297 



region. But the cords of aged persons who do not exhibit the symptoms 

 of paralysis agitans show similar changes, though usually they are not so 

 evident, and hence the pathological anatomy of this disease resolves itself into 

 a somewhat premature and excessive senility of the central system. 



Shrinkage, decay, and destruction mark the progress of senescence, and 

 the nervous system as a whole becomes less vigorous in its responses, less 

 capable of repair or extra strain, and less permeable to the nervous impulses 

 that fall upon it ; and it thus breaks down, not into the disconnected elements 

 of the fetus, but into groups of elements, so that its capacities are lost in a 

 fragmentary and uneven way. 



