OLD AGE. 331 



central nerve cells most responsive to prolonged abnormal 

 conditions of the body even when the disease is located 

 quite outside of this system. 1 



The cause of senile changes in nerve cells cannot be 

 given. Could the central system of an aged person be 

 transplanted to the body of one in the prime of life, 

 possessing a vigorous digestion and perfect circulating 

 system, it might be possible to judge how far such 

 changes are the results of defects in the systems on 

 which the nerve elements depend. Many facts suggest 

 that specialisation in the functions of a cell is the first 

 step towards its ultimate destruction, and in that sense 

 the causes of its death should be mainly inherent. The 

 overgrowth by the supporting tissues and intoxication 

 through defective nutrient conditions are of great im- 

 portance to this senile dissolution, but their exact values 

 are necessarily unknown. A dependent system is, how- 

 ever, at the mercy of the others with which it is associated, 

 and hence the changes caused by defects in the latter 

 are to be distinguished from those arising in the former. 

 This is especially important when an attempt is made 

 to test the hypothesis that the capabilities of the central 

 system tend to disappear in an order inverse to that in 

 which they have developed. This statement applies to 

 changes resident in the nerve elements themselves. 

 When it is remembered that the last developed cells 

 are smallest, and have but a small quantity of cytoplasm, 

 that the very tardiness of their development indicates 

 their environment to have been less favourable, and 

 finally that those conditions which retard growth also 

 favour senescence, the hypothesis appears plausible. In 

 looking for the anatomical changes in this instance it is 

 to be remembered that there is no proof- that the inter- 



1 Schaffer, Ungarisches Arch. f. Med., 1893; Pandi, Ungarisches 

 Arch. f. Med. t 1894 ; Popoff, Virchow's Archiv., 1894. 



